Question

I have a model where I want to use a class method to set the default of for a property:

class Organisation(db.Model):
    name=db.StringProperty()
    code=db.StringProperty(default=generate_code())

    @classmethod
    def generate_code(cls):
        import random
        codeChars='ABCDEF0123456789'
        while True: # Make sure code is unique
            code=random.choice(codeChars)+random.choice(codeChars)+\
                    random.choice(codeChars)+random.choice(codeChars)
            if not cls.all().filter('code = ',code).get(keys_only=True):
                return code

But I get a NameError:

NameError: name 'generate_code' is not defined

How can I access generate_code()?

Answer 1

As I said in a comment, I would use a classmethod to act as a factory and always create you entity through there. It keeps things simpler and no nasty hooks to get the behaviour you want.

Here is a quick example.

class Organisation(db.Model):
    name=db.StringProperty()
    code=db.StringProperty()

    @classmethod
    def generate_code(cls):
        import random
        codeChars='ABCDEF0123456789'
        while True: # Make sure code is unique
            code=random.choice(codeChars)+random.choice(codeChars)+\
                    random.choice(codeChars)+random.choice(codeChars)
            if not cls.all().filter('code = ',code).get(keys_only=True):

        return code

    @classmethod
    def make_organisation(cls,*args,**kwargs):
        new_org = cls(*args,**kwargs)
        new_org.code = cls.generate_code()
        return new_org