model_with_signals.py

# -*- coding: utf-8 -*-
#
# Copyright (c) 2009 Zachary Voase
# 
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation
# files (the "Software"), to deal in the Software without
# restriction, including without limitation the rights to use,
# copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following
# conditions:
# 
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
# OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
# HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
# WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
# OTHER DEALINGS IN THE SOFTWARE.

from functools import wraps

from django.db.models import *


VALID_SIGNALS = ['pre_init',
                 'post_init',
                 'pre_save',
                 'post_save',
                 'pre_delete',
                 'post_delete']

class InvalidSignalError(Exception):
    pass

class ModelSignals(object):
    def __init__(self, model):
        self.model = model
    
    def connect(self, signal_name):
        """Generates a decorator to connect signal handlers."""
        if signal_name not in VALID_SIGNALS:
            raise InvalidSignalError
        def decorator(function):
            @wraps(function)
            def wrapper(*args, **kwargs):
                # Remove the 'sender' kwarg because we already know what that is.
                kwargs.pop('sender', None)
                if 'instance' in kwargs:
                    args = (kwargs.pop('instance'),) + args
                return function(*args, **kwargs)
            getattr(signals, signal_name).connect(wrapper, sender=self.model)
            return wrapper
        decorator.__name__ = signal_name
        return decorator
    
    def __getattribute__(self, attribute):
        try:
            return object.__getattribute__(self, attribute)
        except AttributeError:
            if attribute in VALID_SIGNALS:
                return self.connect(attribute)
    
    @classmethod
    def contribute_to_class(cls, class_, name):
        setattr(class_, name, cls(class_))

class ModelWithSignalsBase(base.ModelBase):
    def __new__(cls, name, bases, attrs):
        model = super(ModelWithSignalsBase, cls).__new__(cls, name, bases, attrs)
        model.add_to_class('signals', ModelSignals)
        return model

class ModelWithSignals(Model):
    __metaclass__ = ModelWithSignalsBase
    
    class Meta(object):
        abstract = True