如何在Django+GraphQL中正确处理多对多关系？

我有一个与User模型存在多对多关系的Game模型，代码如下：

class Game(models.Model):
    name = models.CharField(max_length=256, blank=True)
    users = models.ManyToManyField(to=User, blank=True, related_name='games')


class User(AbstractUser):
    email = models.EmailField(max_length=128, verbose_name='email address', blank=False)

我需要将其与GraphQL关联，实现通过mutations读取和修改users字段。现有的Game查询schema不含users字段时可以正常工作：

{
  games {
    edges {
      node {
        id
        name
      }
    }
  }
}

但添加users字段后无法正常工作，原因是数据库中Game表没有users字段，多对多关系由games_game_users中间表维护。请问该如何修改代码实现game.users字段的交互？

假设使用graphene-django实现Django与GraphQL的集成，按以下步骤修改：

1. 定义GraphQL类型，支持查询users字段 #

在Game的GraphQL类型中显式添加users字段，关联已定义的User类型：

import graphene
from graphene_django import DjangoObjectType
from .models import Game, User

class UserType(DjangoObjectType):
    class Meta:
        model = User
        fields = ("id", "username", "email") # 根据需求选择返回字段

class GameType(DjangoObjectType):
    class Meta:
        model = Game
        fields = ("id", "name", "users") # 加入users字段

class Query(graphene.ObjectType):
    games = graphene.List(GameType)

    def resolve_games(root, info, **kwargs):
        return Game.objects.all()

修改后，查询schema即可正常请求users字段：

{
  games {
    edges {
      node {
        id
        name
        users {
          id
          username
          email
        }
      }
    }
  }
}

2. 实现Mutation，支持添加/移除用户与游戏的关联 #

添加用户到游戏 #

class AddUserToGame(graphene.Mutation):
    class Arguments:
        game_id = graphene.ID(required=True)
        user_id = graphene.ID(required=True)

    game = graphene.Field(GameType)

    def mutate(root, info, game_id, user_id):
        game = Game.objects.get(pk=game_id)
        user = User.objects.get(pk=user_id)
        game.users.add(user)
        return AddUserToGame(game=game)

从游戏移除用户 #

class RemoveUserFromGame(graphene.Mutation):
    class Arguments:
        game_id = graphene.ID(required=True)
        user_id = graphene.ID(required=True)

    game = graphene.Field(GameType)

    def mutate(root, info, game_id, user_id):
        game = Game.objects.get(pk=game_id)
        user = User.objects.get(pk=user_id)
        game.users.remove(user)
        return RemoveUserFromGame(game=game)

注册Mutation #

class Mutation(graphene.ObjectType):
    add_user_to_game = AddUserToGame.Field()
    remove_user_from_game = RemoveUserFromGame.Field()

schema = graphene.Schema(query=Query, mutation=Mutation)

Mutation调用示例 #

添加用户到游戏：

mutation {
  addUserToGame(gameId: "1", userId: "2") {
    game {
      id
      name
      users {
        id
        username
      }
    }
  }
}

从游戏移除用户：

mutation {
  removeUserFromGame(gameId: "1", userId: "2") {
    game {
      id
      name
      users {
        id
        username
      }
    }
  }
}

核心说明 #

• Django多对多字段无需直接操作中间表，通过模型的add()/remove()方法即可维护关联，graphene-django会自动处理中间表的数据库操作。
• 只要在GraphQL类型中正确关联模型的多对多字段，框架就会自动解析并返回关联数据。

内容的提问来源于stack exchange，提问作者Narek