(cross-posted from
StackOverflow<http://stackoverflow.com/questions/15249306/django-conditionally-defined-model-field-in-abstract-model>,
answer there if you prefer, but I thought it might be too low level to get
much help there alone)
I've got an abstract model in my project that I want to use to define a
field by default on concrete subclasses, but also to allow that field to be
redefined as something other than the default dynamically. All of this
works right now:
class classproperty(object):
"""
Decorator for making class properties
"""
def __init__(self, fget):
self.fget = fget
def __get__(self, owner_self, owner_cls):
return self.fget(owner_cls)
class BaseModel(models.Model):
class Meta(object):
abstract = True
@classproperty
def _special_attribute_field(self):
return getattr(self, '_bm_special_attribute_field', 'default')
@property
def bm_special_attribute(self):
return getattr(self, self._special_attribute_field)
...and then there are a bunch of methods that use the latter two functions
to figure out which field to access.
The problem is that right now, classes inheriting from `BaseModel` have to
define the `default` field explicitly, even if they don't use
`_bm_special_attribute_field` to specify something other than the default.
What I'd like to do is add code to `BaseModel` to programmatically define
`default` on concrete submodels *only if* those models don't use
`_bm_special_attribute_field` to change it to something else, in which
case, they should bring their own field. Is there a way to do this,
perhaps with metaclasses? The key thing being that it has to not muck up
the Django machinery.
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