Django custom field gives an error when editing in admin -

i'm trying implement custom django field keep in db name of 1 of model classes (e. g. "cat", "dog", "restaurant", "superprivatecommercialdatapiece", etc.) , return class object when requested:

class cat(models.model):     ...  class somedatapiece(models.model):     relatedto = mygloriousfieldtype(null=true)  ...  newpiece = somedatapiece() newpiece.relatedto = cat print newpiece.relatedto # should print <class 'myproj.myapp.models.cat'> 

and i've made this. i've subclassed models.field, set __metaclass__, etc.:

class mygloriousfieldtype(models.field):      description = "no description, gloriosity."      __metaclass__ = models.subfieldbase      def __init__(self, *args, **kwargs):         kwargs['max_length'] = 40         super(blocktypefield, self).__init__(*args, **kwargs)      def db_type(self, connection):         return 'char(40)'      def to_python(self, value):         if not value:             return none         elif inspect.isclass(value) , issubclass(value, models.model):             return value         elif hasattr(myproj.myapp.models, value):             return getattr(myproj.myapp.models, value)         else:             raise validationerror("invalid model name string")      def get_db_prep_value(self, value, **kwargs):         if inspect.isclass(value) , issubclass(value, models.model):             return value.__name__         else:             # never raised             raise validationerror("invalid value, model subclass expected")      def value_to_string(self, instance):         value = self._get_val_from_obj(obj)         return self.get_prep_value(value) 

and in code above works expected. i've registered of models containing such fields in admin, , can create such objects; text input created mygloriousfieldtype fields.

the crisis begins when try edit existing object mygloriousfieldtype field. first, fills text field "cat object" instead of "cat". second, when change "cat" , click "save changes" gives error:

typeerror @ /admin/myapp/somedatapiece/3/   unbound method prepare_database_save() must   called cat instance first argument (got    mygloriousfieldtype instance instead) 

so, doing wrong?

well, i've figured out. problem inside django core. fields can't return python objects containing models.field attributes prepare_database_save, otherwise error occures. hack solve return tuple (myclassobject, ) instead of myclassobject in to_python(). odd, can do... maybe i'll try post issue somewhere on django's github page.