Offering up some code: PageAwareParentalManyToManyField

[rgs258]

In cases where a ParentalManyToManyField is defined on a mixin class that's to be inherited in both Wagtail Pages and raw Django Models, the PageAwareParentalManyToManyField may be used. I don't remember where I got this code from (or if I created it or not!), but it works great and I thought I'd share:

class PageAwareParentalManyToManyField(ParentalManyToManyField):
    """
    A ManyToManyField that is aware of if it is being used on a page or a non-page
    model. When uses on a page, it will perform as a ParentalManyToManyField,
    otherwise it will perform as a regular ManyToManyField.
    """

    def contribute_to_class(self, cls, name, **kwargs):
        if issubclass(cls, (AbstractPage, PageBase)):
            super().contribute_to_class(cls, name, **kwargs)
        else:
            super(ParentalManyToManyField, self).contribute_to_class(cls, name,
                                                                     **kwargs)

    def value_from_object(self, obj):
        if isinstance(self.model, (AbstractPage, PageBase)):
            return super().value_from_object(obj)
        else:
            return super(ParentalManyToManyField, self).value_from_object(obj)