Is it possible to define names of model's fields dynamically?

Question

Now I have this code:

class Mymodel(models.Model):
    xxxx_count = ForeignCountField(filter={'foreign_table__xxxx': True})
    yyyy_count = ForeignCountField(filter={'foreign_table__yyyy': True})
    zzzz_count = ForeignCountField(filter={'foreign_table__zzzz': True})
    qqqq_count = ForeignCountField(filter={'foreign_table__qqqq': True})
    ssss_count = ForeignCountField(filter={'foreign_table__ssss': True})
    rrrr_count = ForeignCountField(filter={'foreign_table__rrrr': True})

I want something like this:

class Mymodel(models.Model):
    for code in ['xxxx','yyyy','zzzz','qqqq','ssss','rrrr']:
        setattr(self, '%s_count' % code, ForeignCountField(filter={'foreign_table__%s' % code: True}))

But when I try to do this, error raised: "self doesn't defined". Do I need to put this code into some other place?

Answer 1

Maybe you need to put you're code in the constructor method init of your class.

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

Edit: Sorry this don't work. Maybe you can try looking at This, 'this works with django 0.96. There are some modification that make it hard to adjust it with django version 1.0'.

if you wan't it Dirty and Quick you can try something like this:

class Foo(models.Model):
    letters = ["A", "B", "C"]
    for l in letters:
        exec "%s_count = models.CharField(max_length=255)" % l

Answer 2

The way to automate the creation of multiple class attributes is by writing a metaclass. It'd certainly be possible to subclass Django's ModelBase metaclass and add the functionality you need; but it would also be overkill and probably less maintainable than just writing them out.

Answer 3

I'd like to know a bit more about the design decisions that got you to this point. What is a ForeignCountField and why do you need it? Shouldn't it be a property of the respective tables? (a method on the manager or a classmethod?)

Answer 4

If you want to add fields outside model definition you have to use add_to_class model method:

class Mymodel(models.Model):
    pass

for code in ['xxxx','yyyy','zzzz','qqqq','ssss','rrrr']:
    Mymodel.add_to_class('%s_count' % code, ForeignCountField(filter={'foreign_table__%s' % code: True})))