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<ol class="chapter"><li class="affix"><a href="../index.html">Introduction</a></li><li class="affix"><a href="../quickstart.html">Quickstart</a></li><li class="affix"><a href="../types/index.html">Type System</a></li><li><a href="../types/objects/defining_objects.html"><strong aria-hidden="true">1.</strong> Defining objects</a></li><li><ol class="section"><li><a href="../types/objects/complex_fields.html"><strong aria-hidden="true">1.1.</strong> Complex fields</a></li><li><a href="../types/objects/using_contexts.html"><strong aria-hidden="true">1.2.</strong> Using contexts</a></li><li><a href="../types/objects/error_handling.html"><strong aria-hidden="true">1.3.</strong> Error handling</a></li></ol></li><li><a href="../types/other-index.html"><strong aria-hidden="true">2.</strong> Other types</a></li><li><ol class="section"><li><a href="../types/enums.html"><strong aria-hidden="true">2.1.</strong> Enums</a></li><li><a href="../types/interfaces.html"><strong aria-hidden="true">2.2.</strong> Interfaces</a></li><li><a href="../types/input_objects.html"><strong aria-hidden="true">2.3.</strong> Input objects</a></li><li><a href="../types/scalars.html"><strong aria-hidden="true">2.4.</strong> Scalars</a></li><li><a href="../types/unions.html"><strong aria-hidden="true">2.5.</strong> Unions</a></li></ol></li><li><a href="../schema/schemas_and_mutations.html" class="active"><strong aria-hidden="true">3.</strong> Schemas and mutations</a></li><li><a href="../servers/index.html"><strong aria-hidden="true">4.</strong> Adding A Server</a></li><li><ol class="section"><li><a href="../servers/official.html"><strong aria-hidden="true">4.1.</strong> Official Server Integrations</a></li><li><ol class="section"><li><a href="../servers/warp.html"><strong aria-hidden="true">4.1.1.</strong> Warp</a></li><li><a href="../servers/rocket.html"><strong aria-hidden="true">4.1.2.</strong> Rocket</a></li><li><a href="../servers/iron.html"><strong aria-hidden="true">4.1.3.</strong> Iron</a></li><li><a href="../servers/hyper.html"><strong aria-hidden="true">4.1.4.</strong> Hyper</a></li></ol></li><li><a href="../servers/third-party.html"><strong aria-hidden="true">4.2.</strong> Third Party Integrations</a></li></ol></li><li><a href="../advanced/index.html"><strong aria-hidden="true">5.</strong> Advanced Topics</a></li><li><ol class="section"><li><a href="../advanced/introspection.html"><strong aria-hidden="true">5.1.</strong> Introspection</a></li><li><a href="../advanced/non_struct_objects.html"><strong aria-hidden="true">5.2.</strong> Non-struct objects</a></li><li><a href="../advanced/objects_and_generics.html"><strong aria-hidden="true">5.3.</strong> Objects and generics</a></li><li><a href="../advanced/multiple_ops_per_request.html"><strong aria-hidden="true">5.4.</strong> Multiple operations per request</a></li><li><a href="../advanced/dataloaders.html"><strong aria-hidden="true">5.5.</strong> Dataloaders</a></li><li><a href="../advanced/subscriptions.html"><strong aria-hidden="true">5.6.</strong> Subscriptions</a></li></ol></li></ol>
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<h1 class="menu-title">Juniper - GraphQL Server for Rust</h1>
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<main>
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<a class="header" href="#schemas" id="schemas"><h1>Schemas</h1></a>
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<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>
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<p>A schema consists of three types: a query object, a mutation object, and a subscription object.
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These three define the root query fields, mutations and subscriptions of the schema, respectively.</p>
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<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>
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<p>Both query and mutation objects are regular GraphQL objects, defined like any
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other object in Juniper. The mutation and subscription object, however, is optional since schemas
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can be read-only and without subscriptions as well. If mutations/subscriptions functionality is not needed, consider using <a href="https://docs.rs/juniper/0.14.2/juniper/struct.EmptyMutation.html">EmptyMutation</a>/[EmptySubscription][EmptySubscription].</p>
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<p>In Juniper, the <code>RootNode</code> type represents a schema. You usually don't have to
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create this object yourself: see the framework integrations for <a href="../servers/iron.html">Iron</a>
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and <a href="../servers/rocket.html">Rocket</a> how schemas are created together with the handlers
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themselves.</p>
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<p>When the schema is first created, Juniper will traverse the entire object graph
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and register all types it can find. This means that if you define a GraphQL
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object somewhere but never references it, it will not be exposed in a schema.</p>
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<a class="header" href="#the-query-root" id="the-query-root"><h2>The query root</h2></a>
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<p>The query root is just a GraphQL object. You define it like any other GraphQL
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object in Juniper, most commonly using the <code>object</code> proc macro:</p>
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<pre><pre class="playpen"><code class="language-rust"># use juniper::FieldResult;
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# #[derive(juniper::GraphQLObject)] struct User { name: String }
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struct Root;
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#[juniper::graphql_object]
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impl Root {
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fn userWithUsername(username: String) -> FieldResult<Option<User>> {
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// Look up user in database...
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# unimplemented!()
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}
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}
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# fn main() { }
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</code></pre></pre>
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<a class="header" href="#mutations" id="mutations"><h2>Mutations</h2></a>
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<p>Mutations are <em>also</em> just GraphQL objects. Each mutation is a single field that
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usually performs some mutating side-effect, such as updating a database.</p>
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<pre><pre class="playpen"><code class="language-rust"># use juniper::FieldResult;
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# #[derive(juniper::GraphQLObject)] struct User { name: String }
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struct Mutations;
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#[juniper::graphql_object]
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impl Mutations {
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fn signUpUser(name: String, email: String) -> FieldResult<User> {
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// Validate inputs and save user in database...
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# unimplemented!()
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}
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}
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# fn main() { }
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</code></pre></pre>
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<a class="header" href="#converting-a-rust-schema-to-the-a-hrefhttpsgraphqlorglearnschematype-languagegraphql-schema-languagea" id="converting-a-rust-schema-to-the-a-hrefhttpsgraphqlorglearnschematype-languagegraphql-schema-languagea"><h1>Converting a Rust schema to the <a href="https://graphql.org/learn/schema/#type-language">GraphQL Schema Language</a></h1></a>
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<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>
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<pre><pre class="playpen"><code class="language-rust"># // Only needed due to 2018 edition because the macro is not accessible.
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# #[macro_use] extern crate juniper;
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use juniper::{FieldResult, EmptyMutation, EmptySubscription, RootNode};
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struct Query;
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#[juniper::graphql_object]
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impl Query {
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fn hello(&self) -> FieldResult<&str> {
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Ok("hello world")
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}
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}
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fn main() {
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// Define our schema in Rust.
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let schema = RootNode::new(
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Query,
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EmptyMutation::<()>::new(),
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EmptySubscription::<()>::new(),
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);
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// Convert the Rust schema into the GraphQL Schema Language.
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let result = schema.as_schema_language();
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let expected = "\
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type Query {
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hello: String!
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}
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schema {
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query: Query
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}
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";
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assert_eq!(result, expected);
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}
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</code></pre></pre>
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<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
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compile times.</p>
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<!--TODO: Fix This URL when the EmptySubscription become available in the Documentation -->
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[EmptySubscription]: https://docs.rs/juniper/0.14.2/juniper/struct.EmptySubscription.html
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