# This file was copied from django.db.models.fields.subclassing so that we could
# change the Creator.__set__ behavior. Read the comment below for full details.
"""
Convenience routines for creating non-trivial Field subclasses, as well as
backwards compatibility utilities.
Add SubfieldBase as the __metaclass__ for your Field subclass, implement
to_python() and the other necessary methods and everything will work seamlessly.
"""
class SubfieldBase(type):
"""
A metaclass for custom Field subclasses. This ensures the model's attribute
has the descriptor protocol attached to it.
"""
def __new__(cls, name, bases, attrs):
new_class = super(SubfieldBase, cls).__new__(cls, name, bases, attrs)
new_class.contribute_to_class = make_contrib(
new_class, attrs.get('contribute_to_class')
)
return new_class
class Creator(object):
"""
A placeholder class that provides a way to set the attribute on the model.
"""
def __init__(self, field):
self.field = field
def __get__(self, obj, type=None):
if obj is None:
return self
return obj.__dict__[self.field.name]
def __set__(self, obj, value):
# Usually this would call to_python, but we've changed it to pre_init
# so that we can tell which state we're in. By passing an obj,
# we can definitively tell if a value has already been deserialized
# More: https://github.com/bradjasper/django-jsonfield/issues/33
obj.__dict__[self.field.name] = self.field.pre_init(value, obj)
def make_contrib(superclass, func=None):
"""
Returns a suitable contribute_to_class() method for the Field subclass.
If 'func' is passed in, it is the existing contribute_to_class() method on
the subclass and it is called before anything else. It is assumed in this
case that the existing contribute_to_class() calls all the necessary
superclass methods.
"""
def contribute_to_class(self, cls, name):
if func:
func(self, cls, name)
else:
super(superclass, self).contribute_to_class(cls, name)
setattr(cls, self.name, Creator(self))
return contribute_to_class