Custom Fields proposed implementation

models.py

from django.db import models
from django.contrib.contenttypes.models import ContentType

CUSTOMFIELD_TYPE_CHOICES = (
    ('bool', 'boolean'),
    ('char', 'text'),
    ('int', 'integer'),
    ('float', 'decimal'),
)

class CustomFieldManager(models.Manager):
    def get_for_account_and_object(self, account, obj):
        ctype = ContentType.objects.get_for_model(obj)
        return self.filter(account=account, content_type=ctype)

class CustomField(models.Model):
    account = models.ForeignKey('accounts.Account')
    content_type = models.ForeignKey(ContentType)
    name = models.CharField(max_length=255)
    type = models.CharField(max_length=20, choices=CUSTOMFIELD_TYPE_CHOICES)

    class Meta:
        unique_together = ('account', 'content_type', 'name')

    def __unicode__(self):
        return '[CustomField] %s' % self.name

class CustomFieldValue(models.Model):
    field = models.ForeignKey('customfields.CustomField')
    value = models.CharField(max_length=255)

    def __unicode__(self):
        return self.value