diff options
Diffstat (limited to 'webapp/django/db/models/fields/subclassing.py')
-rw-r--r-- | webapp/django/db/models/fields/subclassing.py | 50 |
1 files changed, 50 insertions, 0 deletions
diff --git a/webapp/django/db/models/fields/subclassing.py b/webapp/django/db/models/fields/subclassing.py new file mode 100644 index 0000000000..10add10739 --- /dev/null +++ b/webapp/django/db/models/fields/subclassing.py @@ -0,0 +1,50 @@ +""" +Convenience routines for creating non-trivial Field subclasses. + +Add SubfieldBase as the __metaclass__ for your Field subclass, implement +to_python() and the other necessary methods and everything will work seamlessly. +""" + +class SubfieldBase(type): + """ + A metaclass for custom Field subclasses. This ensures the model's attribute + has the descriptor protocol attached to it. + """ + def __new__(cls, base, name, attrs): + new_class = super(SubfieldBase, cls).__new__(cls, base, name, attrs) + new_class.contribute_to_class = make_contrib( + attrs.get('contribute_to_class')) + return new_class + +class Creator(object): + """ + A placeholder class that provides a way to set the attribute on the model. + """ + def __init__(self, field): + self.field = field + + def __get__(self, obj, type=None): + if obj is None: + raise AttributeError('Can only be accessed via an instance.') + return obj.__dict__[self.field.name] + + def __set__(self, obj, value): + obj.__dict__[self.field.name] = self.field.to_python(value) + +def make_contrib(func=None): + """ + Returns a suitable contribute_to_class() method for the Field subclass. + + If 'func' is passed in, it is the existing contribute_to_class() method on + the subclass and it is called before anything else. It is assumed in this + case that the existing contribute_to_class() calls all the necessary + superclass methods. + """ + def contribute_to_class(self, cls, name): + if func: + func(self, cls, name) + else: + super(self.__class__, self).contribute_to_class(cls, name) + setattr(cls, self.name, Creator(self)) + + return contribute_to_class |