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<ol class="chapter"><li class="chapter-item expanded affix "><a href="index.html">Introduction</a></li><li class="chapter-item expanded affix "><a href="quickstart.html" class="active">Quickstart</a></li><li class="chapter-item expanded affix "><a href="types/index.html">Type System</a></li><li class="chapter-item expanded "><a href="types/objects/defining_objects.html"><strong aria-hidden="true">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">1.1.</strong> Complex fields</a></li><li class="chapter-item expanded "><a href="types/objects/using_contexts.html"><strong aria-hidden="true">1.2.</strong> Using contexts</a></li><li class="chapter-item expanded "><a href="types/objects/error_handling.html"><strong aria-hidden="true">1.3.</strong> Error handling</a></li></ol></li><li class="chapter-item expanded "><a href="types/other-index.html"><strong aria-hidden="true">2.</strong> Other types</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="types/enums.html"><strong aria-hidden="true">2.1.</strong> Enums</a></li><li class="chapter-item expanded "><a href="types/interfaces.html"><strong aria-hidden="true">2.2.</strong> Interfaces</a></li><li class="chapter-item expanded "><a href="types/input_objects.html"><strong aria-hidden="true">2.3.</strong> Input objects</a></li><li class="chapter-item expanded "><a href="types/scalars.html"><strong aria-hidden="true">2.4.</strong> Scalars</a></li><li class="chapter-item expanded "><a href="types/unions.html"><strong aria-hidden="true">2.5.</strong> Unions</a></li></ol></li></ol>
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<h1 class="menu-title">Juniper - GraphQL Server for Rust</h1>
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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 Juniper.</p>
<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>
<h2 id="installation"><a class="header" href="#installation">Installation</a></h2>
<pre><code class="language-toml">[dependencies]
juniper = &quot;0.15&quot;
</code></pre>
<h2 id="schema-example"><a class="header" href="#schema-example">Schema example</a></h2>
<p>Exposing simple enums and structs as GraphQL is just a matter of adding a custom
derive attribute to them. Juniper includes support for basic Rust types that
naturally map to GraphQL features, such as <code>Option&lt;T&gt;</code>, <code>Vec&lt;T&gt;</code>, <code>Box&lt;T&gt;</code>,
<code>String</code>, <code>f64</code>, and <code>i32</code>, references, and slices.</p>
<p>For more advanced mappings, Juniper provides multiple macros to map your Rust
types to a GraphQL schema. The most important one is the
<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
resolvers, which you will use for the <code>Query</code> and <code>Mutation</code> roots.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused_variables)]
</span><span class="boring">extern crate juniper;
</span><span class="boring">use std::fmt::Display;
</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(&amp;self) -&gt; FieldResult&lt;DatabasePool&gt; { Ok(DatabasePool) }
</span><span class="boring"> fn find_human(&amp;self, _id: &amp;str) -&gt; FieldResult&lt;Human&gt; { Err(&quot;&quot;)? }
</span><span class="boring"> fn insert_human(&amp;self, _human: &amp;NewHuman) -&gt; FieldResult&lt;Human&gt; { Err(&quot;&quot;)? }
</span><span class="boring">}
</span>
#[derive(GraphQLEnum)]
enum Episode {
NewHope,
Empire,
Jedi,
}
#[derive(GraphQLObject)]
#[graphql(description = &quot;A humanoid creature in the Star Wars universe&quot;)]
struct Human {
id: String,
name: String,
appears_in: Vec&lt;Episode&gt;,
home_planet: String,
}
// There is also a custom derive for mapping GraphQL input objects.
#[derive(GraphQLInputObject)]
#[graphql(description = &quot;A humanoid creature in the Star Wars universe&quot;)]
struct NewHuman {
name: String,
appears_in: Vec&lt;Episode&gt;,
home_planet: String,
}
// Now, we create our root Query and Mutation types with resolvers by using the
// object macro.
// Objects can have contexts that allow accessing shared state like a database
// pool.
struct Context {
// Use your real database pool here.
pool: DatabasePool,
}
// To make our context usable by Juniper, we have to implement a marker trait.
impl juniper::Context for Context {}
struct Query;
#[graphql_object(
// Here we specify the context type for the object.
// We need to do this in every type that
// needs access to the context.
context = Context,
)]
impl Query {
fn apiVersion() -&gt; &amp;'static str {
&quot;1.0&quot;
}
// Arguments to resolvers can either be simple types or input objects.
// To gain access to the context, we specify a argument
// that is a reference to the Context type.
// Juniper automatically injects the correct context here.
fn human(context: &amp;Context, id: String) -&gt; FieldResult&lt;Human&gt; {
// Get a db connection.
let connection = context.pool.get_connection()?;
// Execute a db query.
// Note the use of `?` to propagate errors.
let human = connection.find_human(&amp;id)?;
// Return the result.
Ok(human)
}
}
// Now, we do the same for our Mutation type.
struct Mutation;
#[graphql_object(
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 createHuman&lt;S: ScalarValue + Display&gt;(context: &amp;Context, new_human: NewHuman) -&gt; FieldResult&lt;Human, S&gt; {
let db = context.pool.get_connection().map_err(|e| e.map_scalar_value())?;
let human: Human = db.insert_human(&amp;new_human).map_err(|e| e.map_scalar_value())?;
Ok(human)
}
}
// A root schema consists of a query, a mutation, and a subscription.
// Request queries can be executed against a RootNode.
type Schema = juniper::RootNode&lt;'static, Query, Mutation, EmptySubscription&lt;Context&gt;&gt;;
<span class="boring">
</span><span class="boring">fn main() {
</span><span class="boring"> let _ = Schema::new(Query, Mutation{}, EmptySubscription::new());
</span><span class="boring">}
</span></code></pre></pre>
<p>We now have a very simple but functional schema for a GraphQL server!</p>
<p>To actually serve the schema, see the guides for our various <a href="./servers/index.html">server integrations</a>.</p>
<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>
<h2 id="executor"><a class="header" href="#executor">Executor</a></h2>
<p>You can invoke <code>juniper::execute</code> directly to run a GraphQL query:</p>
<pre><pre class="playground"><code class="language-rust"><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, EmptyMutation, EmptySubscription, FieldResult,
GraphQLEnum, Variables, graphql_value,
};
#[derive(GraphQLEnum, Clone, Copy)]
enum Episode {
NewHope,
Empire,
Jedi,
}
// Arbitrary context data.
struct Ctx(Episode);
impl juniper::Context for Ctx {}
struct Query;
#[graphql_object(context = Ctx)]
impl Query {
fn favoriteEpisode(context: &amp;Ctx) -&gt; FieldResult&lt;Episode&gt; {
Ok(context.0)
}
}
// A root schema consists of a query, a mutation, and a subscription.
// Request queries can be executed against a RootNode.
type Schema = juniper::RootNode&lt;'static, Query, EmptyMutation&lt;Ctx&gt;, EmptySubscription&lt;Ctx&gt;&gt;;
fn main() {
// Create a context object.
let ctx = Ctx(Episode::NewHope);
// Run the executor.
let (res, _errors) = juniper::execute_sync(
&quot;query { favoriteEpisode }&quot;,
None,
&amp;Schema::new(Query, EmptyMutation::new(), EmptySubscription::new()),
&amp;Variables::new(),
&amp;ctx,
).unwrap();
// Ensure the value matches.
assert_eq!(
res,
graphql_value!({
&quot;favoriteEpisode&quot;: &quot;NEW_HOPE&quot;,
})
);
}
</code></pre></pre>
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