Federation

Support for GraphQL Federation is enabled by default. If you add one of the federation annotations, the corresponding directives will be declared to your schema and the additional Federation queries will be added automatically. You can also disable Federation completely by setting the smallrye.graphql.federation.enabled config key to false.

You can add the Federation directives by using the equivalent Java annotation, e.g. to extend a Product entity with a price field, you can write a class:

package org.example.price;

import org.eclipse.microprofile.graphql.Id;

import io.smallrye.graphql.api.federation.Extends;
import io.smallrye.graphql.api.federation.Key;

@Extends @Key(fields = @FieldSet("id"))
public class Product {
    @Id
    private String id;

    @Description("The price in cent")
    private Integer price;

    // getters and setters omitted
}

And a normal query method that takes the key fields as a parameter and returns the requested type:

package org.example.price;

import org.eclipse.microprofile.graphql.GraphQLApi;
import org.eclipse.microprofile.graphql.Id;
import org.eclipse.microprofile.graphql.Query;

@GraphQLApi
public class Prices {
    @Query
    public Product product(@Id String id) {
        return ...
    }
}

The GraphQL Schema then contains:

type Product @extends @key(fields : "id") {
    id: ID
    price: Int
}

union _Entity = Product

type Query {
    _entities(representations: [_Any!]!): [_Entity]!
    _service: _Service!
    product(id: ID): Product
}

If you can resolve, e.g., the product with different types of ids, you can add multiple @Key annotations.

Federation Batch Resolver

For better performance, there is the option to use batch resolvers with federation. This is not activated on default. It can be activated by setting smallrye.graphql.federation.batchResolving.enabled config key to true.

It is not needed to provide batch resolvers for all entities, if there is no batch resolver, a non-batch resolver is used.

package org.example.price;

import org.eclipse.microprofile.graphql.GraphQLApi;
import org.eclipse.microprofile.graphql.Id;
import org.eclipse.microprofile.graphql.Query;

@GraphQLApi
public class Prices {
    @Query
    public List<Product> product(@Id List<String> id) {
        return ...
    }
}

It is crucial that the sequence of argument list matches with the order of result list. Currently, the name of the Argument id must match with the property name in the type.