product.py

@strawberry.federation.type(keys=["id"])
class UserType:
    id: strawberry.ID = strawberry.federation.field

    @classmethod
    def resolve_reference(cls, id: strawberry.ID):
        return UserType(id)

@strawberry.federation.type(keys=["id"], description="User Type definition")
class ProductType:
    id: strawberry.ID
    name: str

    @strawberry.field
    def created_by(self) -> UserType:

        return UserType(id=self.created_by)
      
@strawberry.type
class Mutation:

    @strawberry.mutation
    def product_create(self, name: str, created_by: int) -> ProductType:

        product = Product(name=name, created_by: int)
        db.session.add(product)
        db.session.commit()

        return product

schema = strawberry.federation.Schema(query=Query, types=[UserType, ProductType], mutation=Mutation, enable_federation_2=True)

user.py

### User microservice

@strawberry.federation.type(keys=["id"])
class UserType:
    id: strawberry.ID
    name: str

    @classmethod
    def resolve_reference(cls, id: strawberry.ID) -> "UserType":

        logger.error(id)
        user = db.session.query(User).get(id)

        return UserType(id=user.id, name=user.name)
      
@strawberry.type
class Mutation:

    @strawberry.mutation
    def user_create(self, info: strawberry.types.Info, name: str) -> UserType:

        user = User(name=name)
        db.session.add(user)
        db.session.commit()

        return user

schema = strawberry.federation.Schema(query=Query, types=[UserType], mutation=Mutation, enable_federation_2=True)