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< h1 class = "menu-title" > Juniper Book (GraphQL server for Rust)< / h1 >
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< h1 id = "schemas" > < a class = "header" href = "#schemas" > Schemas< / a > < / h1 >
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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 >
< p > A schema consists of three types: a query object, a mutation object, and a subscription object.
These three define the root query fields, mutations and subscriptions of the schema, respectively.< / p >
< 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 >
< p > Both query and mutation objects are regular GraphQL objects, defined like any
other object in Juniper. The mutation and subscription objects, however, are optional since schemas
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can be read-only and do not require subscriptions. If mutation/subscription functionality is not needed, consider using < a href = "https://docs.rs/juniper/0.14.2/juniper/struct.EmptyMutation.html" > EmptyMutation< / a > /< a href = "https://docs.rs/juniper/0.14.2/juniper/struct.EmptySubscription.html" > EmptySubscription< / a > .< / p >
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< p > In Juniper, the < code > RootNode< / code > type represents a schema. When the schema is first created,
Juniper will traverse the entire object graph
and register all types it can find. This means that if you define a GraphQL
object somewhere but never reference it, it will not be exposed in a schema.< / p >
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< h2 id = "the-query-root" > < a class = "header" href = "#the-query-root" > The query root< / a > < / h2 >
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< p > The query root is just a GraphQL object. You define it like any other GraphQL
object in Juniper, most commonly using the < code > graphql_object< / code > proc macro:< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > #![allow(unused_variables)]
< / span > < span class = "boring" > extern crate juniper;
< / span > < span class = "boring" > use juniper::{graphql_object, FieldResult, GraphQLObject};
< / span > < span class = "boring" > #[derive(GraphQLObject)] struct User { name: String }
< / span > struct Root;
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#[graphql_object]
impl Root {
fn userWithUsername(username: String) -> FieldResult< Option< User> > {
// Look up user in database...
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< span class = "boring" > unimplemented!()
< / span > }
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}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() { }
< / span > < / code > < / pre > < / pre >
< h2 id = "mutations" > < a class = "header" href = "#mutations" > Mutations< / a > < / h2 >
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< p > Mutations are < em > also< / em > just GraphQL objects. Each mutation is a single field
that performs some mutating side-effect such as updating a database.< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > #![allow(unused_variables)]
< / span > < span class = "boring" > extern crate juniper;
< / span > < span class = "boring" > use juniper::{graphql_object, FieldResult, GraphQLObject};
< / span > < span class = "boring" > #[derive(GraphQLObject)] struct User { name: String }
< / span > struct Mutations;
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#[graphql_object]
impl Mutations {
fn signUpUser(name: String, email: String) -> FieldResult< User> {
// Validate inputs and save user in database...
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< span class = "boring" > unimplemented!()
< / span > }
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}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() { }
< / span > < / code > < / pre > < / pre >
< h1 id = "converting-a-rust-schema-to-the-graphql-schema-language" > < a class = "header" href = "#converting-a-rust-schema-to-the-graphql-schema-language" > Converting a Rust schema to the < a href = "https://graphql.org/learn/schema/#type-language" > GraphQL Schema Language< / a > < / a > < / h1 >
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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 = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > use juniper::{
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graphql_object, EmptyMutation, EmptySubscription, FieldResult, RootNode,
};
struct Query;
#[graphql_object]
impl Query {
fn hello(& self) -> FieldResult< & str> {
Ok(" hello world" )
}
}
fn main() {
// Define our schema in Rust.
let schema = RootNode::new(
Query,
EmptyMutation::< ()> ::new(),
EmptySubscription::< ()> ::new(),
);
// Convert the Rust schema into the GraphQL Schema Language.
let result = schema.as_schema_language();
let expected = " \
type Query {
hello: String!
}
schema {
query: Query
}
" ;
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< span class = "boring" > #[cfg(not(target_os = " windows" ))]
< / span > assert_eq!(result, expected);
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}
< / code > < / pre > < / pre >
< 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
compile times.< / p >
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