Quirks when overriding SQLObject setters

Let's suppose you have a User that is, optionally, a member of a Company. In SQLObject you model it somehow like this:

    class Company(SQLObject):
        name = UnicodeCol(length=16, alternateID=True, alternateMethodName="by_name")
        display_name = UnicodeCol(length=255)

    class User(InheritableSQLObject):
        company = ForeignKey("Company", notNull=False, cascade='null')

Then you want to implement a user settings interface that uses a Select box to choose the company of the user.

For the Select widget to properly handle the validator for your data, you need to put a number in the first option. As my first option, I want to have the "None" entry, so I decided to use -1 to mean "None".

Now, to make it all blend nicely, I overrode the company setter to accept -1 and silently convert it to a None:

    class User(InheritableSQLObject):
        company = ForeignKey("Company", notNull=False, cascade='null')

        def _set_company(self, id):
            "Set the company id, using None if -1 is given"
            if id == -1: id = None
            self._SO_set_company(id)

In the controller, after parsing and validating all the various keyword arguments, I do something like this:

            user.set(**kw)

Now, the overridden method didn't get called.

After some investigation, and with the help of NandoFlorestan on IRC, we figured out the following things:

1. That method needs to be rewritten as _set_companyID:

           def _set_companyID(self, id):
               "Set the company id, using None if -1 is given"
               if id == -1: id = None
               self._SO_set_companyID(id)
   

2. Methods overridden in that way are alsop called by user.set(**kw), but not by the User(**kw) constructor, so using, for example, a similar override to transparently encrypt passwords would give you plaintext passwords for new users and encrypted passwords after they changed it.