Can someone give me an example of extending a ForeignKey model field? I tried like this:
class ForeignKeyField(forms.ModelChoiceField):
def __init__(self, *args, **kwargs):
super(ForeignKeyField, self).__init__(Chain.objects.all(), *args, **kwargs)
def clean(self, value):
return Chain.objects.get(pk=value)
class CustomForeignKey(models.ForeignKey):
description = "key from ndb"
__metaclass__ = models.SubfieldBase
def __init__(self, *args, **kwargs):
super(CustomForeignKey, self).__init__(*args, **kwargs)
def db_type(self, connection):
return "ndb"
def to_python(self, value):
# import pdb; pdb.set_trace()
from google.appengine.api.datastore_types import Key
if isinstance(value, Key) is True:
return value.id()
if value is None:
return
return value
def get_db_prep_save(self, value, connection, prepared=False):
save_value = ndb.Key(API_Chain, value.id).to_old_key()
return save_value
def formfield(self, **kwargs):
return models.Field.formfield(self,ForeignKeyField, **kwargs)
I don't know why but if i use __metaclass__ = models.SubfieldBase the to_python gets called with None values and it says that foreign key cannot be null. If I inherit from models.Field it works but not as a foreign Key.
I would like to see how one can extend the functionality of models.ForeignKey. Thanks.
