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<h1 class="menu-title">Juniper - GraphQL Server for Rust</h1>
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<main>
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<h1><a class="header" href="#quickstart" id="quickstart">Quickstart</a></h1>
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<p>This page will give you a short introduction to the concepts in Juniper.</p>
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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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<h2><a class="header" href="#installation" id="installation">Installation</a></h2>
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<p>!FILENAME Cargo.toml</p>
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<pre><code class="language-toml">[dependencies]
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juniper = { git = "https://github.com/graphql-rust/juniper" }
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</code></pre>
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<h2><a class="header" href="#schema-example" id="schema-example">Schema example</a></h2>
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<p>Exposing simple enums and structs as GraphQL is just a matter of adding a custom
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derive attribute to them. Juniper includes support for basic Rust types that
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naturally map to GraphQL features, such as <code>Option<T></code>, <code>Vec<T></code>, <code>Box<T></code>,
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<code>String</code>, <code>f64</code>, and <code>i32</code>, references, and slices.</p>
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<p>For more advanced mappings, Juniper provides multiple macros to map your Rust
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types to a GraphQL schema. The most important one is the
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<a href="https://docs.rs/juniper/latest/juniper/macro.graphql_object.html">graphql_object</a> procedural macro that is used for declaring an object with
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resolvers, which you will use for the <code>Query</code> and <code>Mutation</code> roots.</p>
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<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused_variables)]
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</span><span class="boring">extern crate juniper;
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</span><span class="boring">use std::fmt::Display;
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</span>use juniper::{
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graphql_object, EmptySubscription, FieldResult, GraphQLEnum,
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GraphQLInputObject, GraphQLObject, ScalarValue,
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};
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<span class="boring">
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</span><span class="boring">struct DatabasePool;
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</span><span class="boring">impl DatabasePool {
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</span><span class="boring"> fn get_connection(&self) -> FieldResult<DatabasePool> { Ok(DatabasePool) }
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</span><span class="boring"> fn find_human(&self, _id: &str) -> FieldResult<Human> { Err("")? }
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</span><span class="boring"> fn insert_human(&self, _human: &NewHuman) -> FieldResult<Human> { Err("")? }
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</span><span class="boring">}
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</span>
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#[derive(GraphQLEnum)]
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enum Episode {
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NewHope,
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Empire,
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Jedi,
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}
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#[derive(GraphQLObject)]
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#[graphql(description = "A humanoid creature in the Star Wars universe")]
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struct Human {
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id: String,
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name: String,
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appears_in: Vec<Episode>,
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home_planet: String,
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}
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// There is also a custom derive for mapping GraphQL input objects.
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#[derive(GraphQLInputObject)]
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#[graphql(description = "A humanoid creature in the Star Wars universe")]
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struct NewHuman {
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name: String,
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appears_in: Vec<Episode>,
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home_planet: String,
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}
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// Now, we create our root Query and Mutation types with resolvers by using the
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// object macro.
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// Objects can have contexts that allow accessing shared state like a database
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// pool.
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struct Context {
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// Use your real database pool here.
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pool: DatabasePool,
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}
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// To make our context usable by Juniper, we have to implement a marker trait.
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impl juniper::Context for Context {}
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struct Query;
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#[graphql_object(
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// Here we specify the context type for the object.
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// We need to do this in every type that
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// needs access to the context.
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context = Context,
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)]
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impl Query {
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fn apiVersion() -> &str {
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"1.0"
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}
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// Arguments to resolvers can either be simple types or input objects.
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// To gain access to the context, we specify a argument
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// that is a reference to the Context type.
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// Juniper automatically injects the correct context here.
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fn human(context: &Context, id: String) -> FieldResult<Human> {
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// Get a db connection.
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let connection = context.pool.get_connection()?;
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// Execute a db query.
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// Note the use of `?` to propagate errors.
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let human = connection.find_human(&id)?;
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// Return the result.
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Ok(human)
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}
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}
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// Now, we do the same for our Mutation type.
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struct Mutation;
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#[graphql_object(
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context = Context,
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// If we need to use `ScalarValue` parametrization explicitly somewhere
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// in the object definition (like here in `FieldResult`), we should
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// declare an explicit type parameter for that, and specify it.
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scalar = S,
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)]
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impl<S: ScalarValue + Display> Mutation {
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fn createHuman(context: &Context, new_human: NewHuman) -> FieldResult<Human, S> {
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let db = context.pool.get_connection().map_err(|e| e.map_scalar_value())?;
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let human: Human = db.insert_human(&new_human).map_err(|e| e.map_scalar_value())?;
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Ok(human)
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}
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}
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// A root schema consists of a query, a mutation, and a subscription.
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// Request queries can be executed against a RootNode.
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type Schema = juniper::RootNode<'static, Query, Mutation, EmptySubscription<Context>>;
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<span class="boring">
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</span><span class="boring">fn main() {
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</span><span class="boring"> let _ = Schema::new(Query, Mutation{}, EmptySubscription::new());
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</span><span class="boring">}
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</span></code></pre></pre>
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<p>We now have a very simple but functional schema for a GraphQL server!</p>
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<p>To actually serve the schema, see the guides for our various <a href="./servers/index.html">server integrations</a>.</p>
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<p>Juniper is a library that can be used in many contexts--it does not require a server and it does not have a dependency on a particular transport or serialization format. You can invoke the executor directly to get a result for a query:</p>
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<h2><a class="header" href="#executor" id="executor">Executor</a></h2>
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<p>You can invoke <code>juniper::execute</code> directly to run a GraphQL query:</p>
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<pre><pre class="playground"><code class="language-rust"><span class="boring">// Only needed due to 2018 edition because the macro is not accessible.
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</span><span class="boring">#[macro_use] extern crate juniper;
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</span>use juniper::{
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graphql_object, EmptyMutation, EmptySubscription, FieldResult,
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GraphQLEnum, Variables,
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};
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#[derive(GraphQLEnum, Clone, Copy)]
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enum Episode {
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NewHope,
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Empire,
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Jedi,
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}
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// Arbitrary context data.
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struct Ctx(Episode);
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impl juniper::Context for Ctx {}
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struct Query;
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#[graphql_object(context = Ctx)]
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impl Query {
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fn favoriteEpisode(context: &Ctx) -> FieldResult<Episode> {
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Ok(context.0)
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}
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}
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// A root schema consists of a query, a mutation, and a subscription.
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// Request queries can be executed against a RootNode.
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type Schema = juniper::RootNode<'static, Query, EmptyMutation<Ctx>, EmptySubscription<Ctx>>;
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fn main() {
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// Create a context object.
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let ctx = Ctx(Episode::NewHope);
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// Run the executor.
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let (res, _errors) = juniper::execute_sync(
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"query { favoriteEpisode }",
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None,
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&Schema::new(Query, EmptyMutation::new(), EmptySubscription::new()),
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&Variables::new(),
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&ctx,
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).unwrap();
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// Ensure the value matches.
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assert_eq!(
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res,
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graphql_value!({
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"favoriteEpisode": "NEW_HOPE",
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})
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);
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}
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</code></pre></pre>
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