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<ol class="chapter"><li class="chapter-item expanded "><a href="introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="quickstart.html" class="active"><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/index.html"><strong aria-hidden="true">3.1.</strong> 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/context.html"><strong aria-hidden="true">3.1.2.</strong> Context</a></li><li class="chapter-item expanded "><a href="types/objects/error/index.html"><strong aria-hidden="true">3.1.3.</strong> Error handling</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="types/objects/error/field.html"><strong aria-hidden="true">3.1.3.1.</strong> Field errors</a></li><li class="chapter-item expanded "><a href="types/objects/error/schema.html"><strong aria-hidden="true">3.1.3.2.</strong> Schema errors</a></li></ol></li><li class="chapter-item expanded "><a href="types/objects/generics.html"><strong aria-hidden="true">3.1.4.</strong> Generics</a></li></ol></li><li class="chapter-item expanded "><a href="types/interfaces.html"><strong aria-hidden="true">3.2.</strong> Interfaces</a></li><li class="chapter-item expanded "><a href="types/unions.html"><strong aria-hidden="true">3.3.</strong> Unions</a></li><li class="chapter-item expanded "><a href="types/enums.html"><strong aria-hidden="true">3.4.</strong> Enums</a></li><li class="chapter-item expanded "><a href="types/input_objects.html"><strong aria-hidden="true">3.5.</strong> Input objects</a></li><li class="chapter-item expanded "><a href="types/scalars.html"><strong aria-hidden="true">3.6.</strong> Scalars</a></li></ol></li><li class="chapter-item expanded "><a href="schema/index.html"><strong aria-hidden="true">4.</strong> Schema</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="schema/subscriptions.html"><strong aria-hidden="true">4.1.</strong> Subscriptions</a></li><li class="chapter-item expanded "><a href="schema/introspection.html"><strong aria-hidden="true">4.2.</strong> Introspection</a></li></ol></li><li class="chapter-item expanded "><a href="serve/index.html"><strong aria-hidden="true">5.</strong> Serving</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="serve/batching.html"><strong aria-hidden="true">5.1.</strong> Batching</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/implicit_and_explicit_null.html"><strong aria-hidden="true">6.1.</strong> Implicit and explicit null</a></li><li class="chapter-item expanded "><a href="advanced/n_plus_1.html"><strong aria-hidden="true">6.2.</strong> N+1 problem</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="advanced/dataloader.html"><strong aria-hidden="true">6.2.1.</strong> DataLoader</a></li><li class="chapter-item expanded "><a href="advanced/lookahead.html"><strong aria-hidden="true">6.2.2.</strong> Look-ahead</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="advanced/eager_loading.html"><strong aria-hidden="true">6.2.2.1.</strong> Eager loading</a></li></ol></li></ol></li></ol></li></ol>
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<h1 id="quickstart"><a class="header" href="#quickstart">Quickstart</a></h1>
<p>This page will give you a short introduction to the concepts in <a href="https://docs.rs/juniper">Juniper</a>.</p>
<p><strong><a href="https://docs.rs/juniper">Juniper</a> follows a <a href="https://www.apollographql.com/blog/backend/architecture/schema-first-vs-code-only-graphql#code-only">code-first</a> approach to define a <a href="https://graphql.org">GraphQL</a> schema.</strong></p>
<blockquote>
<p><strong>TIP</strong>: For a <a href="https://www.apollographql.com/blog/backend/architecture/schema-first-vs-code-only-graphql#schema-first">schema-first</a> approach, consider using a <a href="https://docs.rs/juniper-from-schema"><code>juniper-from-schema</code></a> crate for generating a <a href="https://docs.rs/juniper"><code>juniper</code></a>-based code from a <a href="https://graphql.org/learn/schema">schema</a> file.</p>
</blockquote>
<h2 id="installation"><a class="header" href="#installation">Installation</a></h2>
<pre><code class="language-toml">[dependencies]
juniper = "0.16.1"
</code></pre>
<h2 id="schema"><a class="header" href="#schema">Schema</a></h2>
<p>Exposing simple enums and structs as <a href="https://graphql.org">GraphQL</a> types is just a matter of adding a custom <a href="https://doc.rust-lang.org/stable/reference/attributes/derive.html#derive">derive attribute</a> to them. <a href="https://docs.rs/juniper">Juniper</a> includes support for basic <a href="https://www.rust-lang.org">Rust</a> types that naturally map to <a href="https://graphql.org">GraphQL</a> features, such as <code>Option<T></code>, <code>Vec<T></code>, <code>Box<T></code>, <code>Arc<T></code>, <code>String</code>, <code>f64</code>, <code>i32</code>, references, slices and arrays.</p>
<p>For more advanced mappings, <a href="https://docs.rs/juniper">Juniper</a> provides multiple macros to map your <a href="https://www.rust-lang.org">Rust</a> types to a <a href="https://graphql.org/learn/schema">GraphQL schema</a>. The most important one is the <a href="https://docs.rs/juniper/0.16.1/juniper/macro.graphql_object.html"><code>#[graphql_object]</code> attribute</a> that is used for declaring a <a href="https://spec.graphql.org/October2021#sec-Objects">GraphQL object</a> with resolvers (typically used for declaring <a href="https://spec.graphql.org/October2021#sec-Root-Operation-Types"><code>Query</code> and <code>Mutation</code> roots</a>).</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">
</span><span class="boring">use std::fmt::Display;
</span><span class="boring">
</span>use juniper::{
graphql_object, EmptySubscription, FieldResult, GraphQLEnum,
GraphQLInputObject, GraphQLObject, ScalarValue,
};
<span class="boring">
</span><span class="boring">struct DatabasePool;
</span><span class="boring">impl DatabasePool {
</span><span class="boring"> fn get_connection(&self) -> FieldResult<DatabasePool> { Ok(DatabasePool) }
</span><span class="boring"> fn find_human(&self, _id: &str) -> FieldResult<Human> { Err("")? }
</span><span class="boring"> fn insert_human(&self, _human: &NewHuman) -> FieldResult<Human> { Err("")? }
</span><span class="boring">}
</span>
#[derive(GraphQLEnum)]
enum Episode {
NewHope,
Empire,
Jedi,
}
#[derive(GraphQLObject)]
#[graphql(description = "A humanoid creature in the Star Wars universe")]
struct Human {
id: String,
name: String,
appears_in: Vec<Episode>,
home_planet: String,
}
// There is also a custom derive for mapping GraphQL input objects.
#[derive(GraphQLInputObject)]
#[graphql(description = "A humanoid creature in the Star Wars universe")]
struct NewHuman {
name: String,
appears_in: Vec<Episode>,
home_planet: String,
}
// Now, we create our root `Query` and `Mutation` types with resolvers by using
// the `#[graphql_object]` attribute.
// Resolvers can have a context that allows accessing shared state like a
// database pool.
struct Context {
// Use your real database pool here.
db: DatabasePool,
}
// To make our `Context` usable by `juniper`, we have to implement a marker
// trait.
impl juniper::Context for Context {}
struct Query;
// Here we specify the context type for the object.
// We need to do this in every type that needs access to the `Context`.
#[graphql_object]
#[graphql(context = Context)]
impl Query {
// Note, that the field name will be automatically converted to the
// `camelCased` variant, just as GraphQL conventions imply.
fn api_version() -> &'static str {
"1.0"
}
fn human(
// Arguments to resolvers can either be simple scalar types, enums or
// input objects.
id: String,
// To gain access to the `Context`, we specify a `context`-named
// argument referring the correspondent `Context` type, and `juniper`
// will inject it automatically.
context: &Context,
) -> FieldResult<Human> {
// Get a `db` connection.
let conn = context.db.get_connection()?;
// Execute a `db` query.
// Note the use of `?` to propagate errors.
let human = conn.find_human(&id)?;
// Return the result.
Ok(human)
}
}
// Now, we do the same for our `Mutation` type.
struct Mutation;
#[graphql_object]
#[graphql(
context = Context,
// If we need to use `ScalarValue` parametrization explicitly somewhere
// in the object definition (like here in `FieldResult`), we could
// declare an explicit type parameter for that, and specify it.
scalar = S: ScalarValue + Display,
)]
impl Mutation {
fn create_human<S: ScalarValue + Display>(
new_human: NewHuman,
context: &Context,
) -> FieldResult<Human, S> {
let db = context.db.get_connection().map_err(|e| e.map_scalar_value())?;
let human: Human = db.insert_human(&new_human).map_err(|e| e.map_scalar_value())?;
Ok(human)
}
}
// Root schema consists of a query, a mutation, and a subscription.
// Request queries can be executed against a `RootNode`.
type Schema = juniper::RootNode<'static, Query, Mutation, EmptySubscription<Context>>;
<span class="boring">
</span><span class="boring">fn main() {
</span><span class="boring"> _ = Schema::new(Query, Mutation, EmptySubscription::new());
</span><span class="boring">}</span></code></pre></pre>
<p>Now we have a very simple but functional schema for a <a href="https://graphql.org">GraphQL</a> server!</p>
<p>To actually serve the <a href="https://graphql.org/learn/schema">schema</a>, see the guides for our various <a href="serve/index.html">server integrations</a>.</p>
<h2 id="execution"><a class="header" href="#execution">Execution</a></h2>
<p><a href="https://docs.rs/juniper">Juniper</a> is a library that can be used in many contexts: it doesn't require a server, nor it has a dependency on a particular transport or serialization format. You can invoke the <code>juniper::execute()</code> directly to get a result for a <a href="https://graphql.org">GraphQL</a> query:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">// Only needed due to 2018 edition because the macro is not accessible.
</span><span class="boring">#[macro_use] extern crate juniper;
</span>use juniper::{
graphql_object, graphql_value, EmptyMutation, EmptySubscription,
GraphQLEnum, Variables,
};
#[derive(GraphQLEnum, Clone, Copy)]
enum Episode {
// Note, that the enum value will be automatically converted to the
// `SCREAMING_SNAKE_CASE` variant, just as GraphQL conventions imply.
NewHope,
Empire,
Jedi,
}
// Arbitrary context data.
struct Ctx(Episode);
impl juniper::Context for Ctx {}
struct Query;
#[graphql_object]
#[graphql(context = Ctx)]
impl Query {
fn favorite_episode(context: &Ctx) -> Episode {
context.0
}
}
type Schema = juniper::RootNode<'static, Query, EmptyMutation<Ctx>, EmptySubscription<Ctx>>;
fn main() {
// Create a context.
let ctx = Ctx(Episode::NewHope);
// Run the execution.
let (res, _errors) = juniper::execute_sync(
"query { favoriteEpisode }",
None,
&Schema::new(Query, EmptyMutation::new(), EmptySubscription::new()),
&Variables::new(),
&ctx,
).unwrap();
assert_eq!(
res,
graphql_value!({
"favoriteEpisode": "NEW_HOPE",
}),
);
}</code></pre></pre>
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