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< h1 id = "quickstart" > < a class = "header" href = "#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 id = "installation" > < a class = "header" href = "#installation" > Installation< / a > < / h2 >
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< pre > < code class = "language-toml" > [dependencies]
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juniper = " 0.15"
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< / code > < / pre >
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< h2 id = "schema-example" > < a class = "header" href = "#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
derive attribute to them. Juniper includes support for basic Rust types that
naturally map to GraphQL features, such as < code > Option< T> < / code > , < code > Vec< T> < / code > , < code > Box< T> < / 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
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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)]
< / span > < span class = "boring" > extern crate juniper;
< / span > < span class = "boring" > use std::fmt::Display;
< / span > use juniper::{
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graphql_object, EmptySubscription, FieldResult, GraphQLEnum,
GraphQLInputObject, GraphQLObject, ScalarValue,
};
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< 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 >
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#[derive(GraphQLEnum)]
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enum Episode {
NewHope,
Empire,
Jedi,
}
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#[derive(GraphQLObject)]
#[graphql(description = " A humanoid creature in the Star Wars universe" )]
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struct Human {
id: String,
name: String,
appears_in: Vec< Episode> ,
home_planet: String,
}
// There is also a custom derive for mapping GraphQL input objects.
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#[derive(GraphQLInputObject)]
#[graphql(description = " A humanoid creature in the Star Wars universe" )]
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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
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// object macro.
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// 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;
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#[graphql_object(
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// Here we specify the context type for the object.
// We need to do this in every type that
// needs access to the context.
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context = Context,
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)]
impl Query {
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fn apiVersion() -> & 'static str {
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" 1.0"
}
// 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
// that is a reference to the Context type.
// Juniper automatically injects the correct context here.
fn human(context: & Context, id: String) -> FieldResult< Human> {
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// 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(& id)?;
// Return the result.
Ok(human)
}
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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(
context = Context,
// If we need to use `ScalarValue` parametrization explicitly somewhere
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// in the object definition (like here in `FieldResult`), we could
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// declare an explicit type parameter for that, and specify it.
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scalar = S: ScalarValue + Display,
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)]
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impl Mutation {
fn createHuman< S: ScalarValue + Display> (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())?;
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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// 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" >
< / 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 >
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< 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 >
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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 id = "executor" > < a class = "header" href = "#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.
< / span > < span class = "boring" > #[macro_use] extern crate juniper;
< / span > use juniper::{
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graphql_object, EmptyMutation, EmptySubscription, FieldResult,
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GraphQLEnum, Variables, graphql_value,
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};
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#[derive(GraphQLEnum, Clone, Copy)]
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enum Episode {
NewHope,
Empire,
Jedi,
}
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// Arbitrary context data.
struct Ctx(Episode);
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 {
fn favoriteEpisode(context: & Ctx) -> FieldResult< Episode> {
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() {
// Create a context object.
let ctx = Ctx(Episode::NewHope);
// Run the executor.
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let (res, _errors) = juniper::execute_sync(
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" query { favoriteEpisode }" ,
None,
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& Schema::new(Query, EmptyMutation::new(), EmptySubscription::new()),
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& Variables::new(),
& ctx,
).unwrap();
// Ensure the value matches.
assert_eq!(
res,
graphql_value!({
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" favoriteEpisode" : " NEW_HOPE" ,
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})
);
}
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