Exclude related fields in model._meta.get_fields() - django

Question

I have a model currently defined like this:
class Category(models.Model):
ID = models.AutoField()
name = models.CharField()
desc = models.CharField()
Another model Subcategory has a ForeignKey defined on Category.
When I run:
Category._meta.get_fields()
I get:
(<ManyToOneRel: siteapp.subcategory>, <django.db.models.fields.AutoField: ID>, <django.db.models.fields.CharField: name>, <django.db.models.fields.CharField: desc>)
However, I don't want the ManyToOneRel fields; I just want the others.
Currently, I am doing something like this:
from django.db.models.fields.reverse_related import ManyToOneRel
field_list = []
for field in modelClass._meta.get_fields():
if not isinstance(field, ManyToOneRel):
field_list.append(field)
However, is there a better way to do this, with or without using the model _meta API?

Answer 1

You could use the concrete_fields property.
Category._meta.concrete_fields
However this is an internal Django API, and it may be better to use get_fields() with your own filtering, even though it may be a little more verbose.

Answer 2

I had the same issue creating a serializer mixin that treated only GenericRelaTion fields. Unfortunately, when you use the get_fields() the ManyToOneRel in somecases appear principally when you need to get attname of a field. Therefore I created a function that treates this issue skiping all the ManyToOneRel from fields:
def get_generic_relation_fields(self):
"""
This function returns all the GenericRelation
fields needed to return the values that are
related such as polymorphic models.
"""
other_field = [field for field in self.Meta.model._meta.get_fields()]
fields = [field.attname for field in self.Meta.model._meta.get_fields() if not isinstance(field, (ManyToOneRel))]
generic_relation_fields = []
for field in fields:
get_type = self.Meta.model._meta.get_field(field)
field_type = get_type.__class__.__name__
if field_type == "GenericRelation": #<----- change field name to filter different fields.
generic_relation_fields.append(field)
return generic_relation_fields
Usage:
class MyModel(models.Model):
. . .
first_name = GenericRelation(MyUserPolymorphic)
last_name = GenericRelation(MyUserPolymorphic)
whatever = GenericRelation(MyUserPolymorphic)
class MyModelSerializer(serializer.ModelSerializer)
def create(self, validated_data):
fields = [field for field in get_generic_relation_fields(self)]
print("FIELDS ---->", fields)
. . .
output on POST:
FIELDS ----> ['first_name', 'last_name', 'whatever']
However, there I added 'GenericRelation' field you can add other fields to be filtered and treated as you want.

Answer 3

I have been looking for a solution for this, and I've ended up writing my own script which while not the most clean pythonic code, works. I thought to put it here if someone stumbles upon it in the future.
[field for field in fields if str(type(field)) != "<class 'django.db.models.fields.related.ForeignKey'>"]
I have also used this script as follows to get a dict in the format of {field_name:field_value}
{
field.name: (
getattr(self, field.name)
if str(type(field))
!= "<class 'django.db.models.fields.related.ForeignKey'>"
else getattr(self, field.name).id
)
for field in fields
if str(type(field))
!= "<class 'django.db.models.fields.reverse_related.ManyToOneRel'>"}
I had to do an additional check for ForeignKey constraints as usually showing the field value didn't make sense in that case