id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
8394	ModelForm subclasses act differently to ModelForms even if no changes are made	devinj	nobody	"I think this is a consequence of the metaclass it has, and it may not even be something that should be fixed-- maybe this is intended, and I'm doing something stupid. Anyway, I was messing around with ModelAdmin, and wanted to customize the forms for a large group of them, in a common way-- I figured, alright, I can set the form in a superclass. It's normally ModelAdmin, with no Meta inner class, and no model defined, so it should be easy to define on my own without having to redo it with a different Meta inner class for each of my models, right? The problem is that this results in errors (fields that exist supposedly not existing). If I define a 
{{{
class MyModelAdmin(ModelAdmin): form = ModelForm
}}}
, everything works fine. If I define a
{{{
class MyModelForm(ModelForm): pass
class MyModelAdmin(ModelAdmin): form = MyModelForm
}}}
 it breaks. The workaround I tried to use was to, instead of inheriting from ModelForm, create a new ModelForm in parallel (inherit from BaseModelForm and set the metaclass). The only problem is that this means ModelForm is not in the inheritance tree, which means that the metaclass doesn't do what it should (leading to errors about _meta), which means that the only solution I can do is to rewrite (that is, copy-paste and change a single line) the metaclass to instead refer to my form. I believe, in fact, that this metaclass is the whole reason for the problem-- it does something special for ModelForm, but not so for ModelForm subclasses (or perhaps it's the reverse). Attached is an example of this ugly and very flawed (it sort of works, but something's wrong with the media and so on, making the date and time field worthless) workaround, using step two of the tutorial.  I really don't know much about Django, I only started a few weeks ago, so this is diving pretty deep into the innards for me. I'd guess maybe some sort of marker saying ""hey, I'm just like ModelForm"" (abstract = True?) would be great. All I really know is that I don't like the way it is now, since the only sensible way to get around this is to individually define my ModelForms with the Meta class included-- so far as I can tell."	Bug	closed	Forms	dev	Normal	needsinfo			Design decision needed	0	0	0	0	0	0