Automated related ForeignKey Models in ModelSchema

[21adrian1996]

Can related models be handled automatically?

Model

class ExampleModel(models.Model):
    relation = models.ForeignKey(SomeOtherModel, on_delete=models.PROTECT, related_name='example')

ModelSchema

class ExampleSchema(ModelSchema):
   class Config:
       model = models.ExampleModel
       model_fields = ['id', 'relation']

API

@api.post('/example')
def create_example(request, payload: schemas.ExampleSchema):
    pl = payload.dict()
    relation = get_object_or_404(SomeOtherModel, id=payload.relation)
    pl['relation'] = relation
    example = models.ExampleModel.objects.create(**pl)
    return {'id': example.id}

The above example works with the payload {'relation_id': 4} if the object with ID 4 exists.

Question 1 Is there any specific reason why the field has to be named relation_id in the payload and not just relation?

Question 2 In the API, is it really necessary to do

    pl = payload.dict()
    relation = get_object_or_404(SomeOtherModel, id=payload.relation)
    pl['relation'] = relation

or can that be somehow done automatically? It seems that writing the get_object_or_404() is currently needed, or can that be omitted with an other apporach?

[vitalik]

@21adrian1996

well the philosophy for incoming payloads are only to validate types/structure

but the database calls should happen inside the controller function

Maybe try doing this (relation_id instead of relation):

class ExampleSchema(ModelSchema):
   class Config:
       model = models.ExampleModel
       model_fields = ['id', 'relation_id'] # !!!

...
ExampleModel.objects.create(**pl) # I think this should validate relation_id automatically ?

[ghost]

Hi @21adrian1996 and @vitalik

@21adrian1996

well the philosophy for incoming payloads are only to validate types/structure

but the database calls should happen inside the controller function

Maybe try doing this (relation_id instead of relation):

class ExampleSchema(ModelSchema):
   class Config:
       model = models.ExampleModel
       model_fields = ['id', 'relation_id'] # !!!

...
ExampleModel.objects.create(**pl) # I think this should validate relation_id automatically ?

This will yield a ninja.errors.ConfigError: Field(s) {'my_field'} are not in model. I'm having the same "issue". I have to work a lot with foreign key relationships and as far as I see from the documentation I have to solve it for every field manually.

I found one workaround to check if the field is an FK-field via ìs_relation. It feels dirty because of how I hack my way to the FK-model (so if any one of you knows a better way please comment):

class MyModelSchema(ModelSchema):
  class Config:
    model = MyModel
    model_exclude = [ ... ] # lots of exclusions here for safety reasons


@router.post("add")
def add(request, payload: MyModelSchema):
  my_instance = MyModel()
    for k,v in payload.dict().items():
      if my_instance._meta.get_field(k).is_relation:
        target_model = my_instance._meta.get_field(k).target_field.model
        v = target_model.objects.get(pk=v)
      my_instance.__setattr__(k,v)
  my_instance.save()

Do you think this would be a good enhancement? I like the way Django handles database tables in the backend but appending/using _id in some places makes working with APIs cumbersome (which is of course not django-ninjas fault, I really like this project!).

[vitalik]

@fantasticle

.... This will yield a ninja.errors.ConfigError: Field(s) {'my_field'} are not in model.

I think it should not - can you give your example ?

Maybe workaround for you case would be to set FK ids as attributes:

class MyModelSchema(ModelSchema):
  some_relation_id: int
  other_relation_id: int
  class Config:
    model = MyModel
    fields = ['some_char_field']
...

@api.post(...)
def foo(request, payload: MyModelSchema)
      obj = MyModel(**payload.dict())
      obj.save()

[Bouni]

I had the same problem and your workaround using attributes works perfectly fine!

[chrisbodon]

I´m using that workaround but it gets this when I try to post:

ValueError: Cannot assign "18": "Activity.town" must be a "Town" instance.

My code:

URLS.PY

@api.post("/activities", response=ActivitySchema)
def create_activities(request, data: ActivitySchema):
	obj = Activity.objects.create(**data.dict())
	return obj

The data Im trying to post

{icon_id: '6', name: 'mn bnb', highlight: false, town_id: 18}

SCHEMAS.PY

class ActivitySchema(ModelSchema):
	town_id: int = None
	icon_id: int = None
	
	class Config:
		model = Activity
		model_fields = "__all__"

MODELS.PY

class Activity(models.Model):
	town = models.ForeignKey(Town, on_delete=models.CASCADE, null=False)
	icon = models.ForeignKey(MediaIcon, on_delete=models.CASCADE, null=False)
	name = models.CharField(max_length=255, null=False)
	highlight = models.BooleanField(default=False)
	
	def __str__(self):
		return self.name

[vlada1g]

I have the same problem as you. You should put instead of model_fields = "__all__" this line model_exclude = ['town', 'icon']

[cca32]

@fantasticle

.... This will yield a ninja.errors.ConfigError: Field(s) {'my_field'} are not in model.

I think it should not - can you give your example ?

Maybe workaround for you case would be to set FK ids as attributes:

class MyModelSchema(ModelSchema):
  some_relation_id: int
  other_relation_id: int
  class Config:
    model = MyModel
    fields = ['some_char_field']
...

@api.post(...)
def foo(request, payload: MyModelSchema)
      obj = MyModel(**payload.dict())
      obj.save()

I also tried the first approach to receive the same error Field(s) {'department_id'} are not in model <class 'my_ninja.models.Employee'>

the second option with attributes worked for me too! wondering if it'd be worth it to have an option in class Config to auto-handle all Foreign Keys