Unique fields that allow nulls in Django

Question

I have model Foo which has field bar. The bar field should be unique, but allow nulls in it, meaning I want to allow more than one record if bar field is null,

Answer 1

I recently had the same requirement. Instead of subclassing different fields, I chose to override the save() metod on my model (named 'MyModel' below) as follows:

def save(self):
        """overriding save method so that we can save Null to database, instead of empty string (project requirement)"""
        # get a list of all model fields (i.e. self._meta.fields)...
        emptystringfields = [ field for field in self._meta.fields \
                # ...that are of type CharField or Textfield...
                if ((type(field) == django.db.models.fields.CharField) or (type(field) == django.db.models.fields.TextField)) \
                # ...and that contain the empty string
                and (getattr(self, field.name) == "") ]
        # set each of these fields to None (which tells Django to save Null)
        for field in emptystringfields:
            setattr(self, field.name, None)
        # call the super.save() method
        super(MyModel, self).save()