Is it possible to dynamically name attributes in an App Engine Model?

Question

setattr allows you to dynamically name attributes in Python classes. I'm trying to do something similar with an App Engine Model:

class MyModel(db.Model):
    def __init__(self, *args, **kwargs):
        super(MyModel, self).__init__(*args, **kwargs)

        # Doesn't fully work
        setatr(self, 'prop1', db.ListProperty(db.Key))
        setatr(self, 'prop2', db.StringListProperty())

    # Works fully
    # prop1 = db.ListProperty(db.Key))
    # prop2 = db.StringListProperty())

This code compiles, but when I call model.prop1.append(key) later on, I get this error:

AttributeError: 'ListProperty' object has no attribute 'append'

I suspect this is because prop1 is declared in models instead of self.prop1, but I don't fully understand the syntax's significance.

Has anyone accomplished this, or does anyone have any insight into syntactic differences?

Answer 1

This SO question:

• Adding a user supplied property (at runtime) to an instance of Expando class in google app engine?

gives an example of what you want to do.

Answer 2

I think you're looking for the db.Expando class (instead of db.Model).

Answer 3

Not sure but would this work maybe:

class MyModel(db.Model):
    @classmethod
    def new(cls, *args, **kwargs):        
        setattr(cls, 'props1', db.ListProperty(db.Key))
        setattr(cls, 'props2', db.StringListProperty())
        mymodel = cls(*args, **kwargs)
        delattr(cls, 'props1')
        delattr(cls, 'props2')
        return mymodel