[英]Issue joining data in graphene-django with a ManyToMany field
[英]Graphene-django with ManyToMany & through-table
我的應用程序與直通模型有幾個多對多關系,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 中表示這些數據而沒有成員資格的中間類型(選項 A)似乎很直觀:
{
"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
},
...
]
}
]
}
}
對比選項 B:
{
"data": {
"persons": [
{
"id": "1",
"name": "Jack",
"memberships": [
{
"id": 9,
"date_joined": "2019-01-01"
"group": {
"id": 3,
"name": "Students"
}
},
...
]
}
]
}
}
我找不到任何關於如何使用 (django-)graphene 實現選項 A 的示例。 如何做到這一點,是否支持開箱即用?
兩種方法的優缺點是什么? 數據也需要經常變異,它會改變判決嗎?
您可以通過創建一個表示來自兩個模型的字段的類型來實現這一點。 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
對於從 Graphene 的ObjectType (它是DjangoObjectType 的后代)構建的任何類型,要在輸出中表達一個字段,您需要做兩件事:
DjangoObjectType
評估您提供的模型以自動生成這些模型,並使用fields 屬性讓您自定義要顯示的屬性。
通過自定義fields
,然后為要添加的內容添加手動道具/解析器,您可以使類型返回您想要的任何內容。
請注意,解析器不會接收self
作為第一個參數,而是獲取值 object 。 值對象是查詢解析器的返回值,通常是模型的實例或與過濾器匹配的模型數組等。
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