A schema consists of two types: a query object and a mutation object (Juniper does not support subscriptions yet). These two define the root query fields and mutations of the schema, respectively.

Both query and mutation objects are regular GraphQL objects, defined like any other object in Juniper. The mutation object, however, is optional since schemas can be read-only.

In Juniper, the RootNode type represents a schema. You usually don't have to create this object yourself: see the framework integrations for Iron and Rocket how schemas are created together with the handlers themselves.

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 references it, it will not be exposed in a schema.

The query root is just a GraphQL object. You define it like any other GraphQL object in Juniper, most commonly using the graphql_object! macro:

# use juniper::FieldResult;
# #[derive(juniper::GraphQLObject)] struct User { name: String }
struct Root;

juniper::graphql_object!(Root: () |&self| {
    field userWithUsername(username: String) -> FieldResult<Option<User>> {
        // Look up user in database...
# unimplemented!()
    }
});

# fn main() { }

Mutations are also just GraphQL objects. Each mutation is a single field that usually performs some mutating side-effect, such as updating a database.

# use juniper::FieldResult;
# #[derive(juniper::GraphQLObject)] struct User { name: String }
struct Mutations;

juniper::graphql_object!(Mutations: () |&self| {
    field signUpUser(name: String, email: String) -> FieldResult<User> {
        // Validate inputs and save user in database...
# unimplemented!()
    }
});

# fn main() { }