adminmodel.py

# Adding a semi-dynamic field to Django ModelAdmin
#
# Motivation behind this is to see if django.conf.settings contains a
# setting of some type. I know this could be done with a factory too.
#
# django.forms.Form allows adding extra fields to forms initialization
# time by modifying self.fields dict in __init__. However, ModelAdmin
# only looks at the *class* of the form, not the instance created from
# it, to determine the fields it should draw in the admin interface.
#
# Also: using fields or fieldsets is not an option, as they're are
# checked against the same class's fields, thus raising an exception
# upon init
#
# Basically: adding to self.fields in a form used by ModelAdmin is a
# no-op in Django. I came up with this solution:


from django.contrib import admin
from django.conf import settings
from django import forms

from myapp.models import MyModel

class DynamicFormType(forms.ModelForm.__metaclass__):
    # Akward superclass due to the __all__ variable in django.forms :(
    def __init__(cls, name, bases, dct):
        super(DynamicFormType, cls).__init__(name, bases, dct)
        if getattr(settings, 'APPEND_DYNAMIC_FIELD', False):
            cls.base_fields['dynamic_field'] = forms.CharField()


class MyCustomForm(forms.ModelForm):
    __metaclass__ = DynamicFormType

    model = MyModel

    somefield = forms.CharField()

class MyAdmin(admin.ModelAdmin):
    form = MyCustomForm