1) Yes, it is possible to subclass the ModelBackend. That's not the only step involved in switching from username based logins to email based logins, however, s

1) Yes, it is possible to subclass the ModelBackend. That's not the only step involved in switching from username based logins to email based logins, however, since the default User definition has defined a required username CharField that takes some hackery to get around. 2) Symfony does the same thing with a one to one User <-> Profile relationship. I find this to be a silly hack in both frameworks that creates extra database JOINs for no reason. If I want to place a foreign key on the user table because multiple Users can belong to a single Account, I shouldn't have to go through an additional join table. 3) You can configure Doctrine to raise an exception if you try to save() a model object with invalid fields, and check if the fields are valid at any time with isValid(). It makes a lot more sense to me to do this at the model level since there are many scenarios where you still want validation and aren't actually using forms of any sort.