Interface

Interface is used to abstract Objects with common fields. Async-graphql implements it as a wrapper. The wrapper will forward field resolution to the Object that implements this Interface. Therefore, the Object's fields' type and arguments must match with the Interface's.

Async-graphql implements auto conversion from Object to Interface, you only need to call Into::into.

Interface field names are transformed to camelCase for the schema definition. If you need e.g. a snake_cased GraphQL field name, you can use both the name and method attributes.

  • When name and method exist together, name is the GraphQL field name and the method is the resolver function name.
  • When only name exists, name.to_camel_case() is the GraphQL field name and the name is the resolver function name.

#![allow(unused)]
fn main() {
use async_graphql::*;

struct Circle {
    radius: f32,
}

#[Object]
impl Circle {
    async fn area(&self) -> f32 {
        std::f32::consts::PI * self.radius * self.radius
    }

    async fn scale(&self, s: f32) -> Shape {
        Circle { radius: self.radius * s }.into()
    }

    #[graphql(name = "short_description")]
    async fn short_description(&self) -> String {
        "Circle".to_string()
    }
}

struct Square {
    width: f32,
}

#[Object]
impl Square {
    async fn area(&self) -> f32 {
        self.width * self.width
    }

    async fn scale(&self, s: f32) -> Shape {
        Square { width: self.width * s }.into()
    }

    #[graphql(name = "short_description")]
    async fn short_description(&self) -> String {
        "Square".to_string()
    }
}

#[derive(Interface)]
#[graphql(
    field(name = "area", type = "f32"),
    field(name = "scale", type = "Shape", arg(name = "s", type = "f32")),
    field(name = "short_description", method = "short_description", type = "String")
)]
enum Shape {
    Circle(Circle),
    Square(Square),
}
}

Register the interface manually

Async-graphql traverses and registers all directly or indirectly referenced types from Schema in the initialization phase. If an interface is not referenced, it will not exist in the registry, as in the following example , even if MyObject implements MyInterface, because MyInterface is not referenced in Schema, the MyInterface type will not exist in the registry.


#![allow(unused)]
fn main() {
#[derive(Interface)]
#[graphql(
    field(name = "name", type = "String"),
)]
enum MyInterface {
    MyObject(MyObject),
}

#[derive(SimpleObject)]
struct MyObject {
    name: String,
}

struct Query;

#[Object]
impl Query {
    async fn obj(&self) -> MyObject {
        todo!()
    }
}

type MySchema = Schema<Query, EmptyMutation, EmptySubscription>;
}

You need to manually register the MyInterface type when constructing the Schema:


#![allow(unused)]
fn main() {
Schema::build(Query, EmptyMutation, EmptySubscription)
    .register_type::<MyInterface>()
    .finish();
}