Django & Graphene：如何处理与多态模型的双向关系？

Question

我有一个看起来像这样的 Django 模型（当然是经过简化的）：

from django.db import models
from polymorphic.models import PolymorphicModel

class Tournament(models.Model):
    slug = models.CharField(max_length=100, unique=True)

class Event(PolymorphicModel):
    tournament = models.ForeignKey(Tournament, related_name='events')
    slug = models.CharField(max_length=100)

class PracticeEvent(Event):
    pass

class MatchEvent(Event):
    winner = models.CharField(max_length=100, null=True, blank=True, default=None)

锦标赛由两种项目组成：练习赛和比赛。我想使用 GraphQL，使用 Graphene 公开这个模型。这是我想出的：

import graphene
from graphene_django import DjangoObjectType

from . import models

class TournamentType(DjangoObjectType):
    class Meta:
        model = models.Tournament
        exclude_fields = ('id',)

class EventType(graphene.Interface):
    tournament = graphene.Field(TournamentType, required=True)
    slug = graphene.String(required=True)

class PracticeEventType(DjangoObjectType):
    class Meta:
        model = models.PracticeEvent
        interfaces = (EventType,)
        exclude_fields = ('id',)

class MatchEventType(DjangoObjectType):
    class Meta:
        model = models.MatchEvent
        interfaces = (EventType,)
        exclude_fields = ('id',)

extra_types = {PracticeEventType, MatchEventType}

class Query(graphene.ObjectType):
    tournaments = graphene.List(TournamentType)
    events = graphene.List(EventType)
    # ... resolvers ...

schema = graphene.Schema(
    query=Query,
    types=schema_joust.extra_types,)

到目前为止，还不错；我可以直接查询events { ... }，连tournament都可以。但是，由于没有 DjangoObjectType 和 model = models.Event，我无法查询 tournaments { events {...} }...

我该如何解决这个问题？我无法将 EventType 设为 DjangoObjectTpe，而且我不知道在事后添加 events 字段。

Answer 1

也许 Union 类型是您想要的，结合显式声明 EventType 从接口继承：

import graphene

# Rename your existing EventType to EventTypeInterface and redefine like 
class EventType(DjangoObjectType):
    class Meta:
        model = Event
        interfaces = [EventTypeInterface]


class EventUnionType(graphene.Union):
    @classmethod
    def resolve_type(cls, instance, info):
        if isinstance(instance, MatchEvent):
            return MatchEventType
        elif isinstance(instance, PracticeEvent):
            return PracticeEventType
        return EventType

    class Meta:
        types = [MatchEventType, PracticeEventType, EventType]

Answer 2

就其本身而言，EventType.tournament 和 TournamentType.events 并不难。第一个如题中所示，第二个可以这样实现：

class EventType(graphene.Interface):
    slug = graphene.String(required=True)

class TournamentType(DjangoObjectType):
    class Meta:
        model = models.Tournament
        exclude_fields = ('id',)

    events = graphene.List(EventType)

    def resolve_events(self, info):
        return self.events.all()

graphene-django 无法识别这种关系，但手动声明和解析该字段可以解决问题。为了同时获得 reverse-field，如果我们不需要引用 TournamentType，它就可以工作，我深入研究了 graphene-django 并找到了 graphene_django.converter.convert_django_field_with_choices。这让我们可以这样定义字段：

import graphene
from graphene_django import DjangoObjectType, converter, registry

from . import models

class EventType(graphene.Interface):
    tournament = converter.convert_django_field_with_choices(
        models.Event.tournament.field, registry.get_global_registry())
    slug = graphene.String(required=True)

Django & Graphene：如何处理与多态模型的双向关系？

Django & Graphene: How to handle bidirectional relationship with polmorphic models?

django

graphene-python