Django - MultipleOptionsField - A set of boolean options stored in a positive integer field.

multiple_options_field.py

from django.db.models import SubfieldBase
from django.db.models.fields import PositiveIntegerField

class MultipleOptions(object):
        
    def __init__(self, options, value=None):
        self.options = options

        try:
            self._value = int(value)

        except (ValueError, TypeError):
            self._value = 0

    def _get_flag_value(self, option):
        return (1 << self.options.index(option))
        
    def __getattr__(self, name):
        if name in self.options:
            return bool(self._value & self._get_flag_value(name))

        raise AttributeError("'%s' isn't in '%s'." % (name, '\', '.join(self.options)))

    def __setattr__(self, name, value):
        if not name == 'options' and name in self.options:
            try:
                value = bool(value)

            except (ValueError, TypeError):
                value = False

            current = getattr(self, name)
            if not value == current:
                self._value ^= self._get_flag_value(name)

        else: return super(MultipleOptions, self).__setattr__(name, value)

            
class MultipleOptionsField(PositiveIntegerField):
    
    __metaclass__ = SubfieldBase

    description = "A set of boolean options stored in a positive integer field. "
    
    def __init__(self, options=[], *args, **kwargs): 
        self.options = options
        super(MultipleOptionsField, self).__init__(*args, **kwargs)
    
    def to_python(self, value):
        if isinstance(value, MultipleOptions):
            return value
        
        return MultipleOptions(value=value, options=self.options)

    def get_prep_value(self, value):
        return value._value

tests.py

import unittest

from main import MultipleOptions

class MultipleOptionsTest(unittest.TestCase):
    
    def setUp(self):
        self.options = ['foo', 'bar', 'baz']
        self.container = MultipleOptions(options=self.options)

    def test_attrs(self):
        for option in self.options:
            self.assertTrue(hasattr(self.container, option))
            self.assertTrue(isinstance(getattr(self.container, option), bool))

    def test_get_set(self):
        self.container.foo = True
        self.assertTrue(self.container.foo)
        self.assertEquals(2 ** self.options.index('foo'), self.container._value)

        self.container.foo = False
        self.assertEquals(0, self.container._value)

    def test_get_set_multiple(self):
        self.container.foo = True
        self.assertTrue(self.container.foo)

        self.container.baz = True
        self.assertTrue(self.container.baz)
        self.assertEquals(2 ** self.options.index('foo') \
         + 2 ** self.options.index('baz'), self.container._value)

        self.container.foo = False
        self.assertEquals(2 ** self.options.index('baz'), self.container._value)

        self.container.baz = False
        self.assertEquals(0, self.container._value)
        

main = unittest.main
if __name__ == '__main__': main()

TODO:

• Criar um widget para as opções
• Definir uma maneira para setar os default values (atualmente, estou utilizando o próprio 'default' do PositiveIntegerField, porém dessa maneira as classes client tem que saber que são utilizadas flags binárias, o que não é o ideal)