A related model choice field for Django

gistfile1.py

class RelatedModelChoiceIterator(object):
    def __init__(self, field):
        self.field = field
        self.parent_queryset = field.parent_queryset
        self.queryset = field.queryset
        self.lookup_name = field.lookup_name

    def __iter__(self):
        if self.field.empty_label is not None:
            yield (u"", self.field.empty_label)
        if self.field.cache_choices:
            if self.field.choice_cache is None:
                choices = []
                for obj in self.parent_queryset.all():
                    sub_query = self.queryset.filter(**{self.lookup_name: obj})
                    if len(sub_query) > 0:
                        choices.append((
                            self.field.label_from_instance(obj),
                            [
                                self.choice(sub_obj) for sub_obj in sub_query
                            ]
                        ))
                self.field.choice_cache = choices
            for choice in self.field.choice_cache:
                yield choice
        else:
            for obj in self.parent_queryset.all():
                sub_query = self.queryset.filter(**{self.lookup_name: obj})
                if len(sub_query) > 0:
                    yield (
                        self.field.label_from_instance(obj),
                        [
                            self.choice(sub_obj) for sub_obj in sub_query
                        ]
                    )

    def __len__(self):
        return len(self.parent_queryset)

    def choice(self, obj):
        return (self.field.prepare_value(obj), self.field.label_from_instance(obj))


class RelatedModelChoiceField(forms.ModelChoiceField):

    def __init__(self, parent_queryset, queryset, lookup_name, empty_label=u"---------", cache_choices=False,
                 required=True, widget=None, label=None, initial=None,
                 help_text=None, to_field_name=None, *args, **kwargs):
        self.parent_queryset = parent_queryset
        self.lookup_name = lookup_name
        super(RelatedModelChoiceField, self).__init__(queryset, empty_label, cache_choices,
                required, widget, label, initial,
                help_text, to_field_name, *args, **kwargs)

    def __deepcopy__(self, memo):
        result = super(ChoiceField, self).__deepcopy__(memo)
        result.queryset = result.queryset
        result.parent_queryset = result.parent_queryset
        result.lookup_name = result.lookup_name
        return result

    def _get_choices(self):
        if hasattr(self, '_choices'):
            return self._choices

        return RelatedModelChoiceIterator(self)

    choices = property(_get_choices, ChoiceField._set_choices)

# Usage
class RelatedFieldForm(forms.Form):
    related_field = RelatedModelChoiceField(
        parent_queryset=ParentModel.objects.all(), # Will be used for the optgroups
        queryset=ChildModel.objects.all(), # Will be used for the actual options
        lookup_name='lookup_field' # The name of the field that is the foreign key between the child model and the parent model i.e. ChildModel.lookup_field -> ParentModel
    )

class ManyToManyRelatedModelChoiceIterator(object):
    def __init__(self, field, parent, child):
        self.field = field
        self.queryset = field.queryset
        self.parent = parent
        self.child = child

    def __iter__(self):
        if self.field.empty_label is not None:
            yield (u"", self.field.empty_label)
        if self.field.cache_choices:
            if self.field.choice_cache is None:
                choices = []
                grouper = groupby(self.queryset.select_related(self.parent).select_related(self.child).order_by('%s__name' % self.parent, '%s__name' % self.child), key=lambda x: x.country)
                for k, g in grouper:
                    choices.append(
                        self.field.label_from_instance(k),
                        [
                            self.choice(sub_obj) for sub_obj in g
                        ]
                    )
                self.field.choice_cache = choices
            for choice in self.field.choice_cache:
                yield choice
        else:
            grouper = groupby(self.queryset.select_related(self.parent).select_related(self.child).order_by('%s__name' % self.parent, '%s__name' % self.child), key=lambda x: x.country)
            for k, g in grouper:
                yield (
                    self.field.label_from_instance(k),
                    [
                        self.choice(sub_obj) for sub_obj in g
                    ]
                )

    def __len__(self):
        return len(self.parent_queryset)

    def choice(self, obj):
        return (self.field.prepare_value(obj), self.field.label_from_instance(getattr(obj, self.child)))


class ManyToManyRelatedModelChoiceField(forms.ModelChoiceField):

    def __init__(self, queryset, parent, child, empty_label=u"---------", cache_choices=False,
                 required=True, widget=None, label=None, initial=None,
                 help_text=None, to_field_name=None, *args, **kwargs):
        self.parent = parent
        self.child = child
        super(ManyToManyRelatedModelChoiceField, self).__init__(queryset, empty_label, cache_choices,
                required, widget, label, initial,
                help_text, to_field_name, *args, **kwargs)

    def __deepcopy__(self, memo):
        result = super(ChoiceField, self).__deepcopy__(memo)
        result.queryset = result.queryset
        result.parent = result.parent
        result.child = result.child
        return result

    def _get_choices(self):
        if hasattr(self, '_choices'):
            return self._choices

        return ManyToManyRelatedModelChoiceIterator(self, self.parent, self.child)

    choices = property(_get_choices, ChoiceField._set_choices)

# Usage
class RelatedFieldForm(forms.Form):
    related_field = ManyToManyRelatedModelChoiceField(
        queryset=ThroughModel.objects.all(), # Will be used for the actual options values,
        parent='parent_field', # The parent field of the through model to be used for optgroups
        child='child_field', # The child field of the through model to be used for the options text
    )