CODEWITHSUNDEEP
pythondjangodjango-contenttypes
Yotam Ofek
Yotam Ofek

Reputation: 2408

django-contenttypes - List All Generic Relations for Model

I would like to reflect on a model and list all its backward generic relations.

My model looks like this:

class Service(models.Model):
    host = models.ForeignKey(Host)

    statuses = generic.GenericRelation(Status)

The Status object looks like this:

class Status(TrackedModel):
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey()

    class Meta:
        verbose_name_plural = 'statuses'

I would like to programatically learn that statuses is a generic relation for the Service model. Is this possible? Status._meta.fields does not show statuses, but Status._meta.get_all_field_names() does, only it shows other unwanted things too.

I thought that this might be a possible solution, but it seems really messy to me. I'd love to hear of a better one.

from django.db.models.fields import FieldDoesNotExist
from django.contrib.contenttypes import generic

generic_relations = []
for field_name in Service._meta.get_all_field_names():
    try:
        field = Service._meta.get_field(field_name)
    except FieldDoesNotExist:
        continue

    if isinstance(field, generic.GenericRelation):
        generic_relations.append(field)

Thank you!

Upvotes: 4

Views: 1323

Answers (2)

Elias Prado
Elias Prado

Reputation: 1817

UPDATE 2021:

To list all the GenericRelations() fields:

print(Service._meta.private_fields)

Output:

[<django.contrib.contenttypes.fields.GenericRelation: statuses>]

Nevertheless, if you have more fields with GenericRelations() relationship they will be shown into the output list.

Check the documentation:

https://docs.djangoproject.com/en/3.2/releases/1.10/#id3

Or you can return all of the fields that have a GenericRelation() field type.

ex:

# models.py
class MyModel(models.Model):
    . . .
    my_model_field = GenericRelation(OtherPolyModel)


def get_generic_relation_fields(self):
   """
   This function returns all the GenericRelation 
   fields needed to return the values that are 
   related to a polymorphic model.
   """
   fields = [f.attname for f in self.Meta.model._meta.get_fields()]
   file_fields = []
   for field in fields:
       get_type = self.Meta.model._meta.get_field(field)
       field_type = get_type.__class__.__name__
            
       if field_type == "GenericRelation":
           file_fields.append(field)

       return file_fields

Output:

['my_model_field']

Upvotes: 1

okm
okm

Reputation: 23871

The GenericRelation works similarly as ManyToManyField. You could find it in Service._meta.many_to_many:

filter(lambda f:isinstance(f, generic.GenericRelation), Service._meta.many_to_many)

Upvotes: 3

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