Graphene-django with ManyToMany & through-table

Question

我的应用与直通模型有几个多对多关系，如下所示：

class Person(models.Model):
    name = models.CharField()
class Group(models.Model):
    name = models.CharField()
    members = models.ManyToManyField(Person, through='Membership')
class Membership(models.Model):
    person = models.ForeignKey(Person)
    group = models.ForeignKey(Group)
    date_joined = models.DateField()  # Extra info on the relationship

在 graphql 中表示此数据似乎很直观，而无需使用成员资格的中间类型(选项 A(：

{
  "data": {
    "persons": [
      {
        "id": "1",
        "name": "Jack",
        "groups": [
          {
            "id": 3,                     # From Group-model
            "name": "Students",          # From Group-model
            "date_joined": "2019-01-01"  # From Membership-model
          },
          ...
        ]
      }
    ]
  }
}

与选项 B：

{
  "data": {
    "persons": [
      {
        "id": "1",
        "name": "Jack",
        "memberships": [
          {
            "id": 9,
            "date_joined": "2019-01-01"
            "group": {
              "id": 3, 
              "name": "Students"
            }
          },
          ...
        ]
      }
    ]
  }
}

我找不到任何关于如何使用(django-(石墨烯实现选项A的例子。如何做到这一点，是否支持开箱即用？

这两种方法的优缺点是什么？数据也需要经常变异，它会改变判决吗？

Answer 1

您可以通过创建一个表示来自两个模型的字段的类型来实现此目的。例如：

import graphene
from graphene_django.types import DjangoObjectType

# hybrid type, expresses some characteristics of Member and Group
class UserGroupType(DjangoObjectType):
    class Meta:
        model = Membership
    
        # date_joined is automatically derived from the membership
        # instance, name and id are declared below.
        fields = ('id', 'name', 'date_joined', )
    
    id = graphene.ID()
    name = graphene.String()
    
    def resolve_id(value_obj, info):
        return value_obj.group.pk
    def resolve_name(value_obj, info):
        return value_obj.group.name

class PersonType(DjangoObjectType):
    class Meta:
        model = Person
    
        # id and name are automatically derived from the person
        # instance, groups is declared below, overriding the 
        # normal model relationship.
        fields = ('id', 'name', 'groups', )
    
    groups = graphene.List(UserGroupType)
    
    def resolve_groups(value_obj, info):
        return value_obj.memberships

对于从Graphene的ObjectType(DjangoObjectType衍生而来(构建的任何类型，要在输出中表达字段，您需要两件事：

1. 字段类型的声明
2. 生成要转换为该类型的结果的解析程序方法

DjangoObjectType评估您提供的模型以自动生成这些属性，并使用 fields 属性允许您自定义要显示的属性。

通过自定义fields，然后为要添加的内容添加手动道具/解析器，可以使类型返回您想要的任何内容。

请注意，解析器不会接收 self 作为第一个参数，而是获取值对象。value 对象是查询解析程序的返回值，通常是模型的实例或与筛选器匹配的模型数组等。