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Give us feedback →</a><a class="_text-xs _font-medium _text-gray-500 hover:_text-gray-900 dark:_text-gray-400 dark:hover:_text-gray-100 contrast-more:_text-gray-800 contrast-more:dark:_text-gray-50" href="https://github.com/graphql/graphql.github.io/tree/source/src/pages/learn/schema.mdx">Edit this page</a><button aria-hidden="true" disabled="" class="_flex _items-center _gap-1.5 _transition _opacity-100 disabled:_opacity-0 _text-xs _font-medium _text-gray-500 hover:_text-gray-900 dark:_text-gray-400 dark:hover:_text-gray-100 contrast-more:_text-gray-800 contrast-more:dark:_text-gray-50">Scroll to top<svg fill="none" viewBox="0 0 24 24" stroke="currentColor" class="_-rotate-90 _size-4 _border _rounded-full _border-current"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"></path></svg></button></div></div></nav><div id="reach-skip-nav"></div><article class="_w-full _break-words nextra-content _flex _min-h-[calc(100vh-var(--nextra-navbar-height))] _min-w-0 _justify-center _pb-8 _pr-[calc(env(safe-area-inset-right)-1.5rem)]"><main class="_w-full _min-w-0 _max-w-6xl _px-6 _pt-4 md:_px-12"><div class="nextra-breadcrumb _mt-1.5 _flex _items-center _gap-1 _overflow-hidden _text-sm _text-gray-500 dark:_text-gray-400 contrast-more:_text-current"><div class="_whitespace-nowrap _transition-colors _min-w-[24px] _overflow-hidden _text-ellipsis" title="Learn">Learn</div><svg fill="none" viewBox="0 0 24 24" stroke="currentColor" class="_w-3.5 _shrink-0"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"></path></svg><div class="_whitespace-nowrap _transition-colors _font-medium _text-gray-700 contrast-more:_font-bold contrast-more:_text-current dark:_text-gray-100 contrast-more:dark:_text-current" title="Schemas and Types">Schemas and Types</div></div><h1 class="_mt-2 _text-4xl _font-bold _tracking-tight _text-slate-900 dark:_text-slate-100">Schemas and Types</h1> <p class="learn-subtitle">Learn about the different elements of the GraphQL type system</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">The GraphQL <a href="https://spec.graphql.org/draft/#sec-Type-System" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">type system</a> describes what data can be queried from the API. The collection of those capabilities is referred to as the service’s <em>schema</em> and clients can use that schema to send queries to the API that return predictable results.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">On this page, we’ll explore GraphQL’s <a href="https://spec.graphql.org/draft/#sec-Types" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">six kinds of named type definitions</a> as well as other features of the type system to learn how they may be used to describe your data and the relationships between them. Since GraphQL can be used with any backend framework or programming language, we’ll avoid implementation-specific details and talk only about the concepts.</p> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Type system<a href="#type-system" id="type-system" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">If you’ve seen a GraphQL query before, you know that the GraphQL query language is basically about selecting fields on objects. So, for example, in the following query:</p> <div class="miniGraphiQL"><div class="query-editor"><span class="editor-name rounded-tl">Operation</span></div><div class="result-window"><span class="editor-name rounded-tr">Response</span></div></div> <ol class="[:is(ol,ul)_&]:_my-3 [&:not(:first-child)]:_mt-6 _list-decimal ltr:_ml-6 rtl:_mr-6"> <li class="_my-2">We start with a special “root” object</li> <li class="_my-2">We select the <code class="nextra-code" dir="ltr">hero</code> field on that</li> <li class="_my-2">For the object returned by <code class="nextra-code" dir="ltr">hero</code>, we select the <code class="nextra-code" dir="ltr">name</code> and <code class="nextra-code" dir="ltr">appearsIn</code> fields</li> </ol> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Because the shape of a GraphQL query closely matches the result, we can predict what the query will return without knowing that much about the server. But it’s useful to have an exact description of the data we can request. For example, what fields can we select? What kinds of objects might they return? What fields are available on those sub-objects?</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">That’s where the schema comes in. Every GraphQL service defines a set of types that completely describe the set of possible data we can query on that service. Then, when requests come in, they are validated and executed against that schema.</p> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Type language<a href="#type-language" id="type-language" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">GraphQL services can be written in any language and there are many different approaches you can take when defining the types in a schema:</p> <ul class="[:is(ol,ul)_&]:_my-3 [&:not(:first-child)]:_mt-6 _list-disc ltr:_ml-6 rtl:_mr-6"> <li class="_my-2">Some libraries have you construct the schema types, fields, and resolver functions together using the same programming language that was used to write the GraphQL implementation.</li> <li class="_my-2">Some libraries allow you to define types and fields more ergonomically using what’s commonly called the schema definition language (or SDL) and then write the resolver functions for the corresponding fields separately.</li> <li class="_my-2">Some libraries allow you to write and annotate the resolver functions, and then infer the schema from that.</li> <li class="_my-2">Some libraries may even infer both the types and resolver functions for you, based on some underlying data source(s).</li> </ul> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Since we can’t rely on a specific programming language to discuss GraphQL schemas in this guide, we’ll use SDL because it’s similar to the query language that we’ve seen so far and allows us to talk about GraphQL schemas in a language-agnostic way.</p> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Object types and fields<a href="#object-types-and-fields" id="object-types-and-fields" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">The most basic components of a GraphQL schema are <a href="https://spec.graphql.org/draft/#sec-Objects" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">Object types</a>, which just represent a kind of object you can fetch from your service, and what fields it has. In SDL, we represent it like this:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> appearsIn</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Episode</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">The language is readable, but let’s go over it so that we can have a shared vocabulary:</p> <ul class="[:is(ol,ul)_&]:_my-3 [&:not(:first-child)]:_mt-6 _list-disc ltr:_ml-6 rtl:_mr-6"> <li class="_my-2"><code class="nextra-code" dir="ltr">Character</code> is a <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/schema/#object-types-and-fields">GraphQL Object type</a>, meaning it’s a type with some fields. Most of the types in your schema will be Object types.</li> <li class="_my-2"><code class="nextra-code" dir="ltr">name</code> and <code class="nextra-code" dir="ltr">appearsIn</code> are <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/schema/#object-types-and-fields">fields</a> on the <code class="nextra-code" dir="ltr">Character</code> type. That means that <code class="nextra-code" dir="ltr">name</code> and <code class="nextra-code" dir="ltr">appearsIn</code> are the only fields that can appear in any part of a GraphQL query that operates on the <code class="nextra-code" dir="ltr">Character</code> type.</li> <li class="_my-2"><code class="nextra-code" dir="ltr">String</code> is one of the built-in <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/schema/#scalar-types">Scalar types</a>. These are types that resolve to a single scalar value and can’t have sub-selections in the query. We’ll go over Scalar types more later.</li> <li class="_my-2"><code class="nextra-code" dir="ltr">String!</code> means that the field is a <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/schema/#non-null">Non-Null type</a>, meaning the GraphQL service promises to give you a value whenever you query this field. In SDL, we represent those with an exclamation mark.</li> <li class="_my-2"><code class="nextra-code" dir="ltr">[Episode!]!</code> represents an <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/schema/#list">List type</a> of <code class="nextra-code" dir="ltr">Episode</code> objects. When a List is Non-Null, you can always expect an array (with zero or more items) when you query the <code class="nextra-code" dir="ltr">appearsIn</code> field. In this case, since <code class="nextra-code" dir="ltr">Episode!</code> is also Non-Null within the list, you can always expect every item in the array to be an <code class="nextra-code" dir="ltr">Episode</code> object.</li> </ul> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Now you know what a GraphQL Object type looks like and how to read the basics of SDL.</p> <h3 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-8 _text-2xl">Arguments<a href="#arguments" id="arguments" class="subheading-anchor" aria-label="Permalink for this section"></a></h3> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Every field on a GraphQL Object type can have zero or more <a href="https://spec.graphql.org/draft/#sec-Field-Arguments" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">arguments</a>, for example, the <code class="nextra-code" dir="ltr">length</code> field below:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Starship</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">ID</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> length</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">(</span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70">unit</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">LengthUnit</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> =</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> METER</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">): </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Float</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">All arguments are named. Unlike languages such as JavaScript and Python where functions take a list of ordered arguments, all arguments in GraphQL are passed by name specifically. In this case, the <code class="nextra-code" dir="ltr">length</code> field has one defined argument called <code class="nextra-code" dir="ltr">unit</code>.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Arguments can be either required or optional. When an argument is optional, we can define a <em>default value</em>. If the <code class="nextra-code" dir="ltr">unit</code> argument is not passed, then it will be set to <code class="nextra-code" dir="ltr">METER</code> by default.</p> <h3 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-8 _text-2xl">The Query, Mutation, and Subscription types<a href="#the-query-mutation-and-subscription-types" id="the-query-mutation-and-subscription-types" class="subheading-anchor" aria-label="Permalink for this section"></a></h3> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Every GraphQL schema must support <code class="nextra-code" dir="ltr">query</code> operations. The <em>entry point</em> for this <a href="https://spec.graphql.org/draft/#sec-Root-Operation-Types" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">root operation type</a> is a regular Object type called <code class="nextra-code" dir="ltr">Query</code> by default. So if you see a query that looks like this:</p> <div class="miniGraphiQL"><div class="query-editor"><span class="editor-name rounded-tl">Operation</span></div><div class="result-window"><span class="editor-name rounded-tr">Response</span></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">That means that the GraphQL service needs to have a <code class="nextra-code" dir="ltr">Query</code> type with a <code class="nextra-code" dir="ltr">droid</code> field:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Query</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> droid</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">(</span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70">id</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">ID</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">): </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Droid</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Schemas may also support <code class="nextra-code" dir="ltr">mutation</code> and <code class="nextra-code" dir="ltr">subscription</code> operations by adding additional <code class="nextra-code" dir="ltr">Mutation</code> and <code class="nextra-code" dir="ltr">Subscription</code> types and then defining fields on the corresponding root operation types.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">It’s important to remember that other than the special status of being entry points into the schema, the <code class="nextra-code" dir="ltr">Query</code>, <code class="nextra-code" dir="ltr">Mutation</code>, and <code class="nextra-code" dir="ltr">Subscription</code> types are the same as any other GraphQL Object type, and their fields work exactly the same way.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">You can name your root operation types differently too; if you choose to do so then you will need to inform GraphQL of the new names using the <code class="nextra-code" dir="ltr">schema</code> keyword:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">schema</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> query</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">MyQueryType</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> mutation</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">MyMutationType</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> subscription</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">MySubscriptionType</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Scalar types<a href="#scalar-types" id="scalar-types" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">A GraphQL Object type has a name and fields, but at some point, those fields must resolve to some concrete data. That’s where the <a href="https://spec.graphql.org/draft/#sec-Scalars" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">Scalar types</a> come in: they represent the leaf values of the query.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">In the following query, the <code class="nextra-code" dir="ltr">name</code> and <code class="nextra-code" dir="ltr">appearsIn</code> fields will resolve to Scalar types:</p> <div class="miniGraphiQL"><div class="query-editor"><span class="editor-name rounded-tl">Operation</span></div><div class="result-window"><span class="editor-name rounded-tr">Response</span></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">We know this because those fields don’t have any sub-fields—they are the leaves of the query.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">GraphQL comes with a set of <a href="https://spec.graphql.org/draft/#sec-Scalars.Built-in-Scalars" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">default Scalar types</a> out of the box:</p> <ul class="[:is(ol,ul)_&]:_my-3 [&:not(:first-child)]:_mt-6 _list-disc ltr:_ml-6 rtl:_mr-6"> <li class="_my-2"><code class="nextra-code" dir="ltr">Int</code>: A signed 32‐bit integer.</li> <li class="_my-2"><code class="nextra-code" dir="ltr">Float</code>: A signed double-precision floating-point value.</li> <li class="_my-2"><code class="nextra-code" dir="ltr">String</code>: A UTF‐8 character sequence.</li> <li class="_my-2"><code class="nextra-code" dir="ltr">Boolean</code>: <code class="nextra-code" dir="ltr">true</code> or <code class="nextra-code" dir="ltr">false</code>.</li> <li class="_my-2"><code class="nextra-code" dir="ltr">ID</code>: A unique identifier, often used to refetch an object or as the key for a cache. The <code class="nextra-code" dir="ltr">ID</code> type is serialized in the same way as a <code class="nextra-code" dir="ltr">String</code>; however, defining it as an <code class="nextra-code" dir="ltr">ID</code> signifies that it is not intended to be human‐readable.</li> </ul> <p class="[&:not(:first-child)]:_mt-6 _leading-7">In most GraphQL service implementations, there is also a way to specify custom Scalar types. For example, we could define a <code class="nextra-code" dir="ltr">Date</code> type:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">scalar</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0"> Date</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Then it’s up to our implementation to define how that type should be serialized, deserialized, and validated. For example, you could specify that the <code class="nextra-code" dir="ltr">Date</code> type should always be serialized into an integer timestamp, and your client should know to expect that format for any date fields.</p> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Enum types<a href="#enum-types" id="enum-types" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7"><a href="https://spec.graphql.org/draft/#sec-Enums" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">Enum types</a>, also known as enumeration types, are a special kind of scalar that is restricted to a particular set of allowed values. This allows you to:</p> <ol class="[:is(ol,ul)_&]:_my-3 [&:not(:first-child)]:_mt-6 _list-decimal ltr:_ml-6 rtl:_mr-6"> <li class="_my-2">Validate that any arguments of this type are one of the allowed values</li> <li class="_my-2">Communicate through the type system that a field will always be one of a finite set of values</li> </ol> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Here’s what an Enum type definition looks like in SDL:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">enum</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Episode</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> NEWHOPE</span></span> <span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> EMPIRE</span></span> <span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> JEDI</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">This means that wherever we use the type <code class="nextra-code" dir="ltr">Episode</code> in our schema, we expect it to be exactly one of <code class="nextra-code" dir="ltr">NEWHOPE</code>, <code class="nextra-code" dir="ltr">EMPIRE</code>, or <code class="nextra-code" dir="ltr">JEDI</code>.</p> <div class="nextra-callout _overflow-x-auto _mt-6 _flex _rounded-lg _border _py-2 ltr:_pr-4 rtl:_pl-4 contrast-more:_border-current contrast-more:dark:_border-current _border-blue-200 _bg-blue-100 _text-blue-900 dark:_border-blue-200/30 dark:_bg-blue-900/30 dark:_text-blue-200"><div class="_select-none _text-xl ltr:_pl-3 ltr:_pr-2 rtl:_pr-3 rtl:_pl-2" style="font-family:"Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol""><svg viewBox="0 0 20 20" fill="currentColor" width="20" height="20" class="_mt-1"><path fill-rule="evenodd" clip-rule="evenodd" d="M18 10a8 8 0 11-16 0 8 8 0 0116 0zm-7-4a1 1 0 11-2 0 1 1 0 012 0zM9 9a1 1 0 000 2v3a1 1 0 001 1h1a1 1 0 100-2v-3a1 1 0 00-1-1H9z"></path></svg></div><div class="_w-full _min-w-0 _leading-7">GraphQL service implementations in various languages will have a language-specific way of dealing with Enum types. In languages that support enums as a first-class citizen, the implementation might take advantage of that; in a language like JavaScript with no enum support, these values might be internally mapped to a set of integers. However, these details don’t leak out to the client, which can operate entirely in terms of the string names of the Enum type’s values.</div></div> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Type modifiers<a href="#type-modifiers" id="type-modifiers" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Types are assumed to be nullable and singular by default in GraphQL. However, when you use these named types in a schema (or in <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/queries/#variables">query variable declarations</a>) you can apply additional <em>type modifiers</em> that will affect the meaning of those values.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">As we saw with the Object type example above, GraphQL supports two type modifiers—the <a href="https://spec.graphql.org/draft/#sec-List" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">List</a> and <a href="https://spec.graphql.org/draft/#sec-Non-Null" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">Non-Null</a> types—and they can be used individually or in combination with each other.</p> <h3 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-8 _text-2xl">Non-Null<a href="#non-null" id="non-null" class="subheading-anchor" aria-label="Permalink for this section"></a></h3> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Let’s look at an example:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Here, we’re using a <code class="nextra-code" dir="ltr">String</code> type and marking it as a Non-Null type by adding an exclamation mark (<code class="nextra-code" dir="ltr">!</code>) after the type name. This means that our server always expects to return a non-null value for this field, and if the resolver produces a null value, then that will trigger a GraphQL execution error, letting the client know that something has gone wrong.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">As we saw in an example above, the Non-Null type modifier can also be used when defining arguments for a field, which will cause the GraphQL server to return a validation error if a null value is passed as that argument:</p> <div class="miniGraphiQL"><div class="query-editor"><span class="editor-name rounded-tl">Operation</span></div><div class="result-window"><span class="editor-name rounded-tr">Response</span></div></div> <h3 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-8 _text-2xl">List<a href="#list" id="list" class="subheading-anchor" aria-label="Permalink for this section"></a></h3> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Lists work in a similar way. We can use a type modifier to mark a type as a List type, which indicates that this field will return an array of that type. In SDL, this is denoted by wrapping the type in square brackets, <code class="nextra-code" dir="ltr">[</code> and <code class="nextra-code" dir="ltr">]</code>. It works the same for arguments, where the validation step will expect an array for that value. Here’s an example:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> appearsIn</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Episode</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">As we see above, the Non-Null and List modifiers can be combined. For example, you can have a List of Non-Null <code class="nextra-code" dir="ltr">String</code> types:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">!]</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">This means that the <em>list itself</em> can be null, but it can’t have any null members. For example, in JSON:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">null</span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> // valid</span></span> <span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [] </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">// valid</span></span> <span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"a"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"b"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">] </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">// valid</span></span> <span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"a"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">null</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"b"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">] </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">// error</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Now, let’s say we defined a Non-Null List of <code class="nextra-code" dir="ltr">String</code> types:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]!</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">This means that the list itself cannot be null, but it can contain null values:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">null</span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> // error</span></span> <span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [] </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">// valid</span></span> <span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"a"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"b"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">] </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">// valid</span></span> <span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"a"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">null</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"b"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">] </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">// valid</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Lastly, you can also have a Non-Null List of Non-Null <code class="nextra-code" dir="ltr">String</code> types:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">!]!</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">This means that the list cannot be null and it cannot contain null values:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">null</span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> // error</span></span> <span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [] </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">// valid</span></span> <span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"a"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"b"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">] </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">// valid</span></span> <span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0">myField</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"a"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">null</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"b"</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">] </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">// error</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">You can arbitrarily nest any number of Non-Null and List modifiers, according to your needs.</p> <div class="nextra-callout _overflow-x-auto _mt-6 _flex _rounded-lg _border _py-2 ltr:_pr-4 rtl:_pl-4 contrast-more:_border-current contrast-more:dark:_border-current _border-blue-200 _bg-blue-100 _text-blue-900 dark:_border-blue-200/30 dark:_bg-blue-900/30 dark:_text-blue-200"><div class="_select-none _text-xl ltr:_pl-3 ltr:_pr-2 rtl:_pr-3 rtl:_pl-2" style="font-family:"Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol""><svg viewBox="0 0 20 20" fill="currentColor" width="20" height="20" class="_mt-1"><path fill-rule="evenodd" clip-rule="evenodd" d="M18 10a8 8 0 11-16 0 8 8 0 0116 0zm-7-4a1 1 0 11-2 0 1 1 0 012 0zM9 9a1 1 0 000 2v3a1 1 0 001 1h1a1 1 0 100-2v-3a1 1 0 00-1-1H9z"></path></svg></div><div class="_w-full _min-w-0 _leading-7">In GraphQL, there is no way to define a type so that the field’s data will only be considered valid if a non-empty list is provided. In other words, <code class="nextra-code" dir="ltr">[]</code> would still be a valid response for a Non-Null List of a Non-Null type.</div></div> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Interface types<a href="#interface-types" id="interface-types" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Like many type systems, GraphQL supports <em>abstract types</em>. The first of these types that we’ll explore is an <a href="https://spec.graphql.org/draft/#sec-Interfaces" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">Interface type</a>, which defines a certain set of fields that a concrete Object type or other Interface type must also include to implement it.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">For example, you could have a <code class="nextra-code" dir="ltr">Character</code> Interface type that represents any character in the Star Wars trilogy:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">interface</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">ID</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> friends</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> appearsIn</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Episode</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">This means that any type that <em>implements</em> <code class="nextra-code" dir="ltr">Character</code> needs to have these exact fields as well as the same arguments and return types.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">For example, here are some types that might implement <code class="nextra-code" dir="ltr">Character</code>:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Human</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583"> implements</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">ID</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> friends</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> appearsIn</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Episode</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> starships</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Starship</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> totalCredits</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Int</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span> <span> </span> <span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Droid</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583"> implements</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">ID</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> friends</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> appearsIn</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Episode</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> primaryFunction</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">You can see that both of these types have all of the fields from the <code class="nextra-code" dir="ltr">Character</code> Interface type, but also bring in extra fields—<code class="nextra-code" dir="ltr">totalCredits</code>, <code class="nextra-code" dir="ltr">starships</code> and <code class="nextra-code" dir="ltr">primaryFunction</code>—that are specific to that particular type of character.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Interface types are useful when you want to return an object or set of objects, but those might be of several different types. For example, note that the following query produces an error:</p> <div class="miniGraphiQL"><div class="query-editor"><span class="editor-name rounded-tl">Operation</span></div><div class="result-window"><span class="editor-name rounded-tr">Response</span></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">The <code class="nextra-code" dir="ltr">hero</code> field returns the type <code class="nextra-code" dir="ltr">Character</code>, which means it might be either a <code class="nextra-code" dir="ltr">Human</code> or a <code class="nextra-code" dir="ltr">Droid</code> depending on the <code class="nextra-code" dir="ltr">episode</code> argument. In the query above, you can only ask for fields that exist on the <code class="nextra-code" dir="ltr">Character</code> Interface type, which doesn’t include <code class="nextra-code" dir="ltr">primaryFunction</code>.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">To ask for a field on a specific Object type, you need to use an <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/queries/#inline-fragments">inline fragment</a>:</p> <div class="miniGraphiQL"><div class="query-editor"><span class="editor-name rounded-tl">Operation</span></div><div class="result-window"><span class="editor-name rounded-tr">Response</span></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Interface types may also implement other Interface types:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">interface</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Node</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">ID</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span> <span> </span> <span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">interface</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Character</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583"> implements</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Node</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">ID</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> friends</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> appearsIn</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Episode</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">]</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Note that Interface types may not implement themselves or contain any cyclic references to each other.</p> <div class="nextra-callout _overflow-x-auto _mt-6 _flex _rounded-lg _border _py-2 ltr:_pr-4 rtl:_pl-4 contrast-more:_border-current contrast-more:dark:_border-current _border-blue-200 _bg-blue-100 _text-blue-900 dark:_border-blue-200/30 dark:_bg-blue-900/30 dark:_text-blue-200"><div class="_select-none _text-xl ltr:_pl-3 ltr:_pr-2 rtl:_pr-3 rtl:_pl-2" style="font-family:"Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol""><svg viewBox="0 0 20 20" fill="currentColor" width="20" height="20" class="_mt-1"><path fill-rule="evenodd" clip-rule="evenodd" d="M18 10a8 8 0 11-16 0 8 8 0 0116 0zm-7-4a1 1 0 11-2 0 1 1 0 012 0zM9 9a1 1 0 000 2v3a1 1 0 001 1h1a1 1 0 100-2v-3a1 1 0 00-1-1H9z"></path></svg></div><div class="_w-full _min-w-0 _leading-7">While types may share common fields in a GraphQL API, that may not always warrant the use of an Interface type to enforce that those fields remain consistently named. Interface types are a powerful way to indicate shared behavior across the types that implement them. When used, they should be semantically meaningful to client developers, just like <code class="nextra-code" dir="ltr">Character</code> is a useful abstraction for humans and droids.</div></div> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Union types<a href="#union-types" id="union-types" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">GraphQL supports a second abstract type called a <a href="https://spec.graphql.org/draft/#sec-Unions" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">Union type</a>. Union types share similarities with Interface types, but they cannot define any shared fields among the constituent types.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">A Union type is defined by indicating its member Object types:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">union</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> SearchResult</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> = </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Human</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> | </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Droid</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> | </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Starship</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Wherever we return a <code class="nextra-code" dir="ltr">SearchResult</code> type in our schema, we might get a <code class="nextra-code" dir="ltr">Human</code>, a <code class="nextra-code" dir="ltr">Droid</code>, or a <code class="nextra-code" dir="ltr">Starship</code>. Note that members of a Union type need to be concrete Object types; you can’t define one using Interface types or other Union types as members.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">In this case, if you query a field that returns the <code class="nextra-code" dir="ltr">SearchResult</code> Union type, you need to use an <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/queries/#inline-fragments">inline fragment</a> to be able to query any fields that are defined on the member Object types:</p> <div class="miniGraphiQL"><div class="query-editor"><span class="editor-name rounded-tl">Operation</span></div><div class="result-window"><span class="editor-name rounded-tr">Response</span></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">The <code class="nextra-code" dir="ltr">__typename</code> field is a special <em>meta-field</em> that automatically exists on every Object type and resolves to the name of that type, providing a way to differentiate between data types on the client.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Also, in this case, since <code class="nextra-code" dir="ltr">Human</code> and <code class="nextra-code" dir="ltr">Droid</code> share a common interface (<code class="nextra-code" dir="ltr">Character</code>), you can query their common fields in one place and still get the same result:</p> <div class="miniGraphiQL"><div class="query-editor"><span class="editor-name rounded-tl">Operation</span></div><div class="result-window"><span class="editor-name rounded-tr">Response</span></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Note that <code class="nextra-code" dir="ltr">name</code> is still specified on <code class="nextra-code" dir="ltr">Starship</code> because otherwise it wouldn’t show up in the results given that <code class="nextra-code" dir="ltr">Starship</code> is not a <code class="nextra-code" dir="ltr">Character</code>!</p> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Input Object types<a href="#input-object-types" id="input-object-types" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Most of the examples we’ve covered on this page demonstrate how Object, Scalar, Enum, Interface, and Union types may be used as <em>output types</em> for the fields in a schema. But we have also seen that field arguments must specify their <em>input types</em>.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">So far, we’ve only talked about using scalar values (like Enums or String types) as an input type for a field argument. However, you can also pass complex objects as arguments using an <a href="https://spec.graphql.org/draft/#sec-Input-Objects" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">Input Object type</a>, which is the last kind of named types in GraphQL that we’ll explore.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">This is particularly valuable in the case of <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/queries/#mutations">mutations</a>, where you might want to pass in a whole object to be created. In SDL, Input Object types look similar to regular Object types, but with the keyword <code class="nextra-code" dir="ltr">input</code> instead of <code class="nextra-code" dir="ltr">type</code>:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">input</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> ReviewInput</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> stars</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Int</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> commentary</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span> <span> </span> <span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Mutation</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> createReview</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">(</span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70">episode</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Episode</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">, </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70">review</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">ReviewInput</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">): </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Review</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Here is how you could use the Input Object type in a mutation:</p> <div class="miniGraphiQL"><div class="query-editor"><span class="editor-name rounded-tl">Operation</span></div><div class="result-window"><span class="editor-name rounded-tr">Response</span></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">The fields on an Input Object type can refer to other Input Object types, but you can’t mix input and output types in your schema. Input Object types also can’t have arguments on their fields.</p> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Directives<a href="#directives" id="directives" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">In certain instances where field arguments are insufficient or certain common behaviors must be replicated in multiple locations, <a href="https://spec.graphql.org/draft/#sec-Type-System.Directives" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">directives</a> allow us to modify parts of a GraphQL schema or operation by using an <code class="nextra-code" dir="ltr">@</code> character followed by the directive’s name.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7"><em>Type system directives</em> allow us to annotate the types, fields, and arguments in a schema so that they may be validated or executed differently.</p> <div class="nextra-callout _overflow-x-auto _mt-6 _flex _rounded-lg _border _py-2 ltr:_pr-4 rtl:_pl-4 contrast-more:_border-current contrast-more:dark:_border-current _border-blue-200 _bg-blue-100 _text-blue-900 dark:_border-blue-200/30 dark:_bg-blue-900/30 dark:_text-blue-200"><div class="_select-none _text-xl ltr:_pl-3 ltr:_pr-2 rtl:_pr-3 rtl:_pl-2" style="font-family:"Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol""><svg viewBox="0 0 20 20" fill="currentColor" width="20" height="20" class="_mt-1"><path fill-rule="evenodd" clip-rule="evenodd" d="M18 10a8 8 0 11-16 0 8 8 0 0116 0zm-7-4a1 1 0 11-2 0 1 1 0 012 0zM9 9a1 1 0 000 2v3a1 1 0 001 1h1a1 1 0 100-2v-3a1 1 0 00-1-1H9z"></path></svg></div><div class="_w-full _min-w-0 _leading-7"><p class="[&:not(:first-child)]:_mt-6 _leading-7">Directives may also be defined for use in GraphQL operations as <em>executable directives</em>. <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/queries/#directives">Read more about executable directives on the Queries page.</a></p></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">The GraphQL specification defines several <a href="https://spec.graphql.org/draft/#sec-Type-System.Directives.Built-in-Directives" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">built-in directives</a>. For example, for implementations that support SDL, the <code class="nextra-code" dir="ltr">@deprecated</code> directive will be available to annotate deprecated parts of the schema:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> fullName</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0"> @deprecated</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">(</span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70">reason</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"Use `fullName`."</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">)</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">While you won’t need to define the <code class="nextra-code" dir="ltr">@deprecated</code> directive in your schema explicitly if you’re using a GraphQL implementation that supports SDL, it’s underlying definition would look like this:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">directive</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0"> @deprecated</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">(</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> reason</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> = </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF">"No longer supported"</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">on</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> FIELD_DEFINITION</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> | </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">ENUM_VALUE</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Note that, just like fields, directives can accept arguments and those arguments can have default values. The <code class="nextra-code" dir="ltr">@deprecated</code> directive has a nullable <code class="nextra-code" dir="ltr">reason</code> argument that accepts a <code class="nextra-code" dir="ltr">String</code> as an input type and falls back to <code class="nextra-code" dir="ltr">"No longer supported"</code>. And with directives, we must specify where they may be used, such as on a <code class="nextra-code" dir="ltr">FIELD_DEFINITION</code> or <code class="nextra-code" dir="ltr">ENUM_VALUE</code> for the <code class="nextra-code" dir="ltr">@deprecated</code> directive.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">In addition to GraphQL’s built-in directives, you may define your own <em>custom directives</em>. As with custom Scalar types, it’s up to your chosen GraphQL implementation to determine how to handle custom directives during query execution.</p> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Documentation<a href="#documentation" id="documentation" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <h3 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-8 _text-2xl">Descriptions<a href="#descriptions" id="descriptions" class="subheading-anchor" aria-label="Permalink for this section"></a></h3> <p class="[&:not(:first-child)]:_mt-6 _leading-7">GraphQL allows you to add documentation to the types, fields, and arguments in a schema. In fact, the GraphQL specification encourages you to do this in all cases unless the name of the type, field, or argument is self-descriptive. Schema descriptions are defined using Markdown syntax and can be multiline or single line.</p> <p class="[&:not(:first-child)]:_mt-6 _leading-7">In SDL, they would look like this:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">"""</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">A character from the Star Wars universe</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">"""</span></span> <span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> "The name of the character."</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span> <span> </span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">"""</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">The episodes in the Star Wars trilogy</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">"""</span></span> <span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">enum</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Episode</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> "Star Wars Episode IV: A New Hope, released in 1977."</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> </span></span> <span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> NEWHOPE</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> "Star Wars Episode V: The Empire Strikes Back, released in 1980."</span></span> <span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> EMPIRE</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> "Star Wars Episode VI: Return of the Jedi, released in 1983."</span></span> <span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> JEDI</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span> <span> </span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">"""</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">The query type, represents all of the entry points into our object graph</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D">"""</span></span> <span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Query</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> """</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> Fetches the hero of a specified Star Wars film.</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> """</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> hero</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">(</span></span> <span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"> "The name of the film that the hero appears in."</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> episode</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Episode</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> ): </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">Character</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">In addition to making a GraphQL API schema more expressive, descriptions are helpful to client developers because they are available in <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/introspection/">introspection queries</a> and visible in developer tools such as <a href="https://github.com/graphql/graphiql" target="_blank" rel="noreferrer" class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]">GraphiQL</a>.</p> <h3 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-8 _text-2xl">Comments<a href="#comments" id="comments" class="subheading-anchor" aria-label="Permalink for this section"></a></h3> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Occasionally, you may need to add comments in a schema that do not describe types, fields, or arguments, and are not meant to be seen by clients. In those cases, you can add a single-line comment to SDL by preceding the text with a <code class="nextra-code" dir="ltr">#</code> character:</p> <div class="nextra-code _relative [&:not(:first-child)]:_mt-6"><pre class="_overflow-x-auto _subpixel-antialiased _text-[.9em] _bg-white dark:_bg-black _py-4 _ring-1 _ring-inset _ring-gray-300 dark:_ring-neutral-700 contrast-more:_ring-gray-900 contrast-more:dark:_ring-gray-50 contrast-more:_contrast-150 _rounded-md" tabindex="0"><code class="nextra-code" dir="ltr"><span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D"># This line is treated like whitespace and ignored by GraphQL</span></span> <span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">type</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF"> Character</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8"> {</span></span> <span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70"> name</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF">String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583">!</span></span> <span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8">}</span></span></code></pre><div class="_opacity-0 _transition [div:hover>&]:_opacity-100 focus-within:_opacity-100 _flex _gap-1 _absolute _right-4 _top-2"><button class="_transition _rounded-md _p-1.5 _border _border-gray-300 dark:_border-neutral-700 contrast-more:_border-gray-900 contrast-more:dark:_border-gray-50 md:_hidden" title="Toggle word wrap"><svg viewBox="0 0 24 24" width="24" height="24" class="_h-4 _w-auto"><path fill="currentColor" d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3l3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"></path></svg></button></div></div> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Comments may also be added to client queries:</p> <div class="miniGraphiQL"><div class="query-editor"><span class="editor-name rounded-tl">Operation</span></div><div class="result-window"><span class="editor-name rounded-tr">Response</span></div></div> <h2 class="_font-semibold _tracking-tight _text-slate-900 dark:_text-slate-100 _mt-10 _border-b _pb-1 _text-3xl _border-neutral-200/70 contrast-more:_border-neutral-400 dark:_border-primary-100/10 contrast-more:dark:_border-neutral-400">Next steps<a href="#next-steps" id="next-steps" class="subheading-anchor" aria-label="Permalink for this section"></a></h2> <p class="[&:not(:first-child)]:_mt-6 _leading-7">To recap what we’ve learned about schemas and types:</p> <ul class="[:is(ol,ul)_&]:_my-3 [&:not(:first-child)]:_mt-6 _list-disc ltr:_ml-6 rtl:_mr-6"> <li class="_my-2">Depending on what library is selected to build a GraphQL service, we can define a schema in a language-agnostic way using SDL or by compiling the schema from the code that provides data for its fields</li> <li class="_my-2">There are six kinds of named type definitions in GraphQL: Object, Scalar, Enum, Interface, Union, and Input Object types</li> <li class="_my-2">Object types contain fields that specify output types, and those fields may have arguments that specify input types</li> <li class="_my-2">The <code class="nextra-code" dir="ltr">Int</code>, <code class="nextra-code" dir="ltr">Float</code>, <code class="nextra-code" dir="ltr">String</code>, <code class="nextra-code" dir="ltr">Boolean</code>, and <code class="nextra-code" dir="ltr">ID</code> Scalar types are built into GraphQL, and you can also define your own custom scalars</li> <li class="_my-2">Like Scalar types, Enum types represent leaf values in a GraphQL schema but they are limited to a finite set of values</li> <li class="_my-2">The List (<code class="nextra-code" dir="ltr">[]</code>) and Non-Null (<code class="nextra-code" dir="ltr">!</code>) type modifiers allow you to change the default behavior for a field’s output type or argument’s input type</li> <li class="_my-2">Interface and Union types are abstract types that allow different concrete Object types to be output from a single field</li> <li class="_my-2">Input Object types allow you to pass more complex values into a field argument or directive argument than Scalar and Enum types allow</li> <li class="_my-2">Type system directives can be applied to the types, fields, and arguments in a schema to alter how they are validated and executed during a query</li> <li class="_my-2">GraphQL supports schema documentation using type, field, and argument descriptions, and it also supports comments that are ignored by the parser</li> </ul> <p class="[&:not(:first-child)]:_mt-6 _leading-7">Now that you understand the key features of the type system, you’re ready to learn more about how to <a class="_text-primary-600 _underline _decoration-from-font [text-underline-position:from-font]" href="/learn/queries/">query data from a GraphQL API</a>.</p><div class="_mt-16"></div><div class="_mb-8 _flex _items-center _border-t _pt-8 dark:_border-neutral-800 contrast-more:_border-neutral-400 dark:contrast-more:_border-neutral-400 print:_hidden"><a title="Introduction" class="_flex _max-w-[50%] _items-center _gap-1 _py-4 _text-base _font-medium _text-gray-600 _transition-colors [word-break:break-word] hover:_text-primary-600 dark:_text-gray-300 md:_text-lg ltr:_pr-4 rtl:_pl-4" href="/learn/"><svg fill="none" viewBox="0 0 24 24" stroke="currentColor" class="_inline _h-5 _shrink-0 ltr:_rotate-180"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"></path></svg>Introduction</a><a title="Queries" class="_flex _max-w-[50%] _items-center _gap-1 _py-4 _text-base _font-medium _text-gray-600 _transition-colors [word-break:break-word] hover:_text-primary-600 dark:_text-gray-300 md:_text-lg ltr:_ml-auto ltr:_pl-4 ltr:_text-right rtl:_mr-auto rtl:_pr-4 rtl:_text-left" href="/learn/queries/">Queries<svg fill="none" 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