<!DOCTYPE HTML>
<html lang="en" class="sidebar-visible no-js light">
<head>
<!-- Book generated using mdBook -->
<meta charset="UTF-8">
<title>Schemas and mutations - Juniper Book (GraphQL server for Rust)</title>
<!-- Custom HTML head -->
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<meta name="description" content="User guide for Juniper (GraphQL server library for Rust).">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="theme-color" content="#ffffff" />
<link rel="icon" href="../favicon.svg">
<link rel="shortcut icon" href="../favicon.png">
<link rel="stylesheet" href="../css/variables.css">
<link rel="stylesheet" href="../css/general.css">
<link rel="stylesheet" href="../css/chrome.css">
<link rel="stylesheet" href="../css/print.css" media="print">
<!-- Fonts -->
<link rel="stylesheet" href="../FontAwesome/css/font-awesome.css">
<link rel="stylesheet" href="../fonts/fonts.css">
<!-- Highlight.js Stylesheets -->
<link rel="stylesheet" href="../highlight.css">
<link rel="stylesheet" href="../tomorrow-night.css">
<link rel="stylesheet" href="../ayu-highlight.css">
<!-- Custom theme stylesheets -->
</head>
<body>
<!-- Provide site root to javascript -->
<script type="text/javascript">
var path_to_root = "../";
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
</script>
<!-- Work around some values being stored in localStorage wrapped in quotes -->
<script type="text/javascript">
try {
var theme = localStorage.getItem('mdbook-theme');
var sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') && theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
</script>
<!-- Set the theme before any content is loaded, prevents flash -->
<script type="text/javascript">
var theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
var html = document.querySelector('html');
html.classList.remove('no-js')
html.classList.remove('light')
html.classList.add(theme);
html.classList.add('js');
</script>
<!-- Hide / unhide sidebar before it is displayed -->
<script type="text/javascript">
var html = document.querySelector('html');
var sidebar = 'hidden';
if (document.body.clientWidth >= 1080) {
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
sidebar = sidebar || 'visible';
}
html.classList.remove('sidebar-visible');
html.classList.add("sidebar-" + sidebar);
</script>
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
<div class="sidebar-scrollbox">
<ol class="chapter"><li class="chapter-item expanded "><a href="../index.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="../quickstart.html"><strong aria-hidden="true">2.</strong> Quickstart</a></li><li class="chapter-item expanded "><a href="../types/index.html"><strong aria-hidden="true">3.</strong> Type System</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../types/objects/defining_objects.html"><strong aria-hidden="true">3.1.</strong> Defining objects</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../types/objects/complex_fields.html"><strong aria-hidden="true">3.1.1.</strong> Complex fields</a></li><li class="chapter-item expanded "><a href="../types/objects/using_contexts.html"><strong aria-hidden="true">3.1.2.</strong> Using contexts</a></li><li class="chapter-item expanded "><a href="../types/objects/error_handling.html"><strong aria-hidden="true">3.1.3.</strong> Error handling</a></li></ol></li><li class="chapter-item expanded "><a href="../types/other-index.html"><strong aria-hidden="true">3.2.</strong> Other types</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../types/enums.html"><strong aria-hidden="true">3.2.1.</strong> Enums</a></li><li class="chapter-item expanded "><a href="../types/interfaces.html"><strong aria-hidden="true">3.2.2.</strong> Interfaces</a></li><li class="chapter-item expanded "><a href="../types/input_objects.html"><strong aria-hidden="true">3.2.3.</strong> Input objects</a></li><li class="chapter-item expanded "><a href="../types/scalars.html"><strong aria-hidden="true">3.2.4.</strong> Scalars</a></li><li class="chapter-item expanded "><a href="../types/unions.html"><strong aria-hidden="true">3.2.5.</strong> Unions</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="../schema/schemas_and_mutations.html" class="active"><strong aria-hidden="true">4.</strong> Schemas and mutations</a></li><li class="chapter-item expanded "><a href="../servers/index.html"><strong aria-hidden="true">5.</strong> Adding A Server</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../servers/official.html"><strong aria-hidden="true">5.1.</strong> Official Server Integrations</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../servers/warp.html"><strong aria-hidden="true">5.1.1.</strong> Warp</a></li><li class="chapter-item expanded "><a href="../servers/rocket.html"><strong aria-hidden="true">5.1.2.</strong> Rocket</a></li><li class="chapter-item expanded "><a href="../servers/iron.html"><strong aria-hidden="true">5.1.3.</strong> Iron</a></li><li class="chapter-item expanded "><a href="../servers/hyper.html"><strong aria-hidden="true">5.1.4.</strong> Hyper</a></li></ol></li><li class="chapter-item expanded "><a href="../servers/third-party.html"><strong aria-hidden="true">5.2.</strong> Third Party Integrations</a></li></ol></li><li class="chapter-item expanded "><a href="../advanced/index.html"><strong aria-hidden="true">6.</strong> Advanced Topics</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../advanced/introspection.html"><strong aria-hidden="true">6.1.</strong> Introspection</a></li><li class="chapter-item expanded "><a href="../advanced/non_struct_objects.html"><strong aria-hidden="true">6.2.</strong> Non-struct objects</a></li><li class="chapter-item expanded "><a href="../advanced/implicit_and_explicit_null.html"><strong aria-hidden="true">6.3.</strong> Implicit and explicit null</a></li><li class="chapter-item expanded "><a href="../advanced/objects_and_generics.html"><strong aria-hidden="true">6.4.</strong> Objects and generics</a></li><li class="chapter-item expanded "><a href="../advanced/multiple_ops_per_request.html"><strong aria-hidden="true">6.5.</strong> Multiple operations per request</a></li><li class="chapter-item expanded "><a href="../advanced/dataloaders.html"><strong aria-hidden="true">6.6.</strong> Dataloaders</a></li><li class="chapter-item expanded "><a href="../advanced/subscriptions.html"><strong aria-hidden="true">6.7.</strong> Subscriptions</a></li></ol></li></ol>
</div>
<div id="sidebar-resize-handle" class="sidebar-resize-handle"></div>
</nav>
<div id="page-wrapper" class="page-wrapper">
<div class="page">
<div id="menu-bar-hover-placeholder"></div>
<div id="menu-bar" class="menu-bar sticky bordered">
<div class="left-buttons">
<button id="sidebar-toggle" class="icon-button" type="button" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
<i class="fa fa-bars"></i>
</button>
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
<i class="fa fa-paint-brush"></i>
</button>
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
<li role="none"><button role="menuitem" class="theme" id="light">Light (default)</button></li>
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
</ul>
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
<i class="fa fa-search"></i>
</button>
</div>
<h1 class="menu-title">Juniper Book (GraphQL server for Rust)</h1>
<div class="right-buttons">
<a href="../print.html" title="Print this book" aria-label="Print this book">
<i id="print-button" class="fa fa-print"></i>
</a>
</div>
</div>
<div id="search-wrapper" class="hidden">
<form id="searchbar-outer" class="searchbar-outer">
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
</form>
<div id="searchresults-outer" class="searchresults-outer hidden">
<div id="searchresults-header" class="searchresults-header"></div>
<ul id="searchresults">
</ul>
</div>
</div>
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
<script type="text/javascript">
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
</script>
<div id="content" class="content">
<main>
<h1 id="schemas"><a class="header" href="#schemas">Schemas</a></h1>
<p>Juniper follows a <a href="https://blog.logrocket.com/code-first-vs-schema-first-development-graphql/">code-first approach</a> to defining GraphQL schemas. If you would like to use a <a href="https://blog.logrocket.com/code-first-vs-schema-first-development-graphql/">schema-first approach</a> instead, consider <a href="https://github.com/davidpdrsn/juniper-from-schema">juniper-from-schema</a> for generating code from a schema file.</p>
<p>A schema consists of three types: a query object, a mutation object, and a subscription object.
These three define the root query fields, mutations and subscriptions of the schema, respectively.</p>
<p>The usage of subscriptions is a little different from the mutation and query objects, so there is a specific <a href="../advanced/subscriptions.html">section</a> that discusses them.</p>
<p>Both query and mutation objects are regular GraphQL objects, defined like any
other object in Juniper. The mutation and subscription objects, however, are optional since schemas
can be read-only and do not require subscriptions. If mutation/subscription functionality is not needed, consider using <a href="https://docs.rs/juniper/0.14.2/juniper/struct.EmptyMutation.html">EmptyMutation</a>/<a href="https://docs.rs/juniper/0.14.2/juniper/struct.EmptySubscription.html">EmptySubscription</a>.</p>
<p>In Juniper, the <code>RootNode</code> type represents a schema. When the schema is first created,
Juniper will traverse the entire object graph
and register all types it can find. This means that if you define a GraphQL
object somewhere but never reference it, it will not be exposed in a schema.</p>
<h2 id="the-query-root"><a class="header" href="#the-query-root">The query root</a></h2>
<p>The query root is just a GraphQL object. You define it like any other GraphQL
object in Juniper, most commonly using the <code>graphql_object</code> proc macro:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused_variables)]
</span><span class="boring">extern crate juniper;
</span><span class="boring">use juniper::{graphql_object, FieldResult, GraphQLObject};
</span><span class="boring">#[derive(GraphQLObject)] struct User { name: String }
</span>struct Root;
#[graphql_object]
impl Root {
fn userWithUsername(username: String) -> FieldResult<Option<User>> {
// Look up user in database...
<span class="boring"> unimplemented!()
</span> }
}
<span class="boring">
</span><span class="boring">fn main() { }
</span></code></pre></pre>
<h2 id="mutations"><a class="header" href="#mutations">Mutations</a></h2>
<p>Mutations are <em>also</em> just GraphQL objects. Each mutation is a single field
that performs some mutating side-effect such as updating a database.</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused_variables)]
</span><span class="boring">extern crate juniper;
</span><span class="boring">use juniper::{graphql_object, FieldResult, GraphQLObject};
</span><span class="boring">#[derive(GraphQLObject)] struct User { name: String }
</span>struct Mutations;
#[graphql_object]
impl Mutations {
fn signUpUser(name: String, email: String) -> FieldResult<User> {
// Validate inputs and save user in database...
<span class="boring"> unimplemented!()
</span> }
}
<span class="boring">
</span><span class="boring">fn main() { }
</span></code></pre></pre>
<h1 id="converting-a-rust-schema-to-the-graphql-schema-language"><a class="header" href="#converting-a-rust-schema-to-the-graphql-schema-language">Converting a Rust schema to the <a href="https://graphql.org/learn/schema/#type-language">GraphQL Schema Language</a></a></h1>
<p>Many tools in the GraphQL ecosystem require the schema to be defined in the <a href="https://graphql.org/learn/schema/#type-language">GraphQL Schema Language</a>. You can generate a <a href="https://graphql.org/learn/schema/#type-language">GraphQL Schema Language</a> representation of your schema defined in Rust using the <code>schema-language</code> feature (on by default):</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">extern crate juniper;
</span>use juniper::{
graphql_object, EmptyMutation, EmptySubscription, FieldResult, RootNode,
};
struct Query;
#[graphql_object]
impl Query {
fn hello(&self) -> FieldResult<&str> {
Ok("hello world")
}
}
fn main() {
// Define our schema in Rust.
let schema = RootNode::new(
Query,
EmptyMutation::<()>::new(),
EmptySubscription::<()>::new(),
);
// Convert the Rust schema into the GraphQL Schema Language.
let result = schema.as_schema_language();
let expected = "\
type Query {
hello: String!
}
schema {
query: Query
}
";
<span class="boring"> #[cfg(not(target_os = "windows"))]
</span> assert_eq!(result, expected);
}
</code></pre></pre>
<p>Note the <code>schema-language</code> feature may be turned off if you do not need this functionality to reduce dependencies and speed up
compile times.</p>
<!--TODO: Fix This URL when the EmptySubscription become available in the Documentation -->
</main>
<nav class="nav-wrapper" aria-label="Page navigation">
<!-- Mobile navigation buttons -->
<a rel="prev" href="../types/unions.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next" href="../servers/index.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
<div style="clear: both"></div>
</nav>
</div>
</div>
<nav class="nav-wide-wrapper" aria-label="Page navigation">
<a rel="prev" href="../types/unions.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next" href="../servers/index.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
</nav>
</div>
<script type="text/javascript">
window.playground_copyable = true;
</script>
<script src="../elasticlunr.min.js" type="text/javascript" charset="utf-8"></script>
<script src="../mark.min.js" type="text/javascript" charset="utf-8"></script>
<script src="../searcher.js" type="text/javascript" charset="utf-8"></script>
<script src="../clipboard.min.js" type="text/javascript" charset="utf-8"></script>
<script src="../highlight.js" type="text/javascript" charset="utf-8"></script>
<script src="../book.js" type="text/javascript" charset="utf-8"></script>
<!-- Custom JS scripts -->
</body>
</html>