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<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>
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<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 -->
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