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

Question

I have a Django model that looks like this (simplified of course):
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)
Tournaments consist of two kinds of events: practice events, and matches. I'd like to expose this model using GraphQL, using Graphene. This is what I have come up with:
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,)
So far, so good; I can query events { ... } directly, and even the tournament is available. However, as there is no DjangoObjectType with model = models.Event, I can't query tournaments { events {...} }...
How can I fix this? I can't make EventType a DjangoObjectTpe, and I don't know to add the events field after the fact.

Answer 1

On their own, EventType.tournament and TournamentType.events aren't so hard. The first one is shown in the question, and the second one can be implemented like this:
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 doesn't recognize the relationship, but declaring and resolving the field manually does the trick. To also get the reverse-field, which would work if we didn't need to reference TournamentType, I digged into graphene-django and found graphene_django.converter.convert_django_field_with_choices. This lets us define the field like this:
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)

Answer 2

Perhaps a Union type is what you want, combined with declaring EventType explicitly to inherit from an interface:
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]