Tag "polymorphic"

Polymorphic inheritance ala SQLAlchemy

This is a different take on polymorphic inheritance, inspired by SQLAlchemy's approach to the problem. The common Django approach (e.g. snippets 1031 & 1034, [django_polymorphic](http://github.com/bconstantin/django_polymorphic)) is to use a foreign key to `ContentType` on the parent model and override `save()` to set the right content type automatically. That works fine but it might not always be possible or desirable, for example if there is another field that determines the "real type" of an instance. In contrast this snippet (which is actually posted and maintained at [gist.github](http://gist.github.com/608595)) allows the user to explicitly specify the field that determines the real type of an instance. The basic idea and the terminology (`polymorphic_on` field, `polymorphic_identity` value) are taken from [SQLAlchemy](http://www.sqlalchemy.org/docs/orm/inheritance.html). Some other features: * It works for proxy child models too, with almost no overhead compared to non-polymorphic managers (since there's no need to hit another DB table as for multi-table inheritance). * It does not override the default (or any other) model Manager. Regular (non-polymorphic) managers and querysets are still available if desired. * It does not require extending a custom Model base class, using a custom metaclass, monkeypatching the models or any kind of magic.