Django multi-table inheritance and graphene

Question

I am trying to serve a graphql endpoint through django-graphene. I have the following models:

class BaseModel(models.Model):
    fk = models.ForeignKey(MainModel, related_name='bases')
    base_info = models.CharField(...)

class ChildModel(BaseModel):
    name = models.CharField(...)

MainModel being my central data model. There are several variants of ChildModel, which explains the multi-table inheritance used here. I have been able to get things to work with this schema declaration:

class BaseModelType(DjangoObjectType):
    class Meta:
        model = BaseModel

class ChildModelType(DjangoObjectType):
    class Meta:
        model = ChildModel

class MainModelType(DjangoObjectType):
    class Meta:
        model = MainModel

which allows the following graphQL query:

{
  mainModel(id: 123) {
    id
    bases {
      id
      baseInfo
      childmodel {
        id
        name
      }
    }
  }
}

However, I'd like to flatten this the way Django understands the inheritance, so that I can query the data like this:

{
  mainModel(id: 123) {
    id
    bases {
      id
      baseInfo
      name        <--- this field from the child is now on the base level
    }
  }
}

I suspect the answer is in how I declare ChildModelType, but I haven't been able to figure it out. Any hints appreciated!

Answer 1

You can do it by declaring additional field and resolve method in BaseModelType class:

class BaseModelType(DjangoObjectType):
    name_from_child = graphene.String()

    class Meta:
        model = BaseModel

    def resolve_name_from_child(self, info):
        # if ChildModel have ForeignKey to BaseModel
        # first_child = self.childmodel_set.first()

        # for your case with multi-table inheritance
        # ChildModel is derived from BaseModel: class ChildModel(BaseModel):
        first_child = self.childmodel

        if first_child:
            return first_child.name
        return None

query:

{
  mainModel(id: 123) {
    id
    bases {
      id
      baseInfo
      name_from_child   <--- first child name
    }
  }
}