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PODjango model class decorator
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copied!<p>I have a need to track changes on Django model instances. I'm aware of solutions like django-reversion but they are overkill for my cause.</p> <p>I had the idea to create a parameterized class decorator to fit this purpose. The arguments are the field names and a callback function. Here is the code I have at this time:</p> <pre><code>def audit_fields(fields, callback_fx): def __init__(self, *args, **kwargs): self.__old_init(*args, **kwargs) self.__old_state = self.__get_state_helper() def save(self, *args, **kwargs): new_state = self.__get_state_helper() for k,v in new_state.items(): if (self.__old_state[k] != v): callback_fx(self, k, self.__old_state[k], v) val = self.__old_save(*args, **kwargs) self.__old_state = self.__get_state_helper() return val def __get_state_helper(self): # make a list of field/values. state_dict = dict() for k,v in [(field.name, field.value_to_string(self)) for field in self._meta.fields if field.name in fields]: state_dict[k] = v return state_dict def fx(clazz): # Stash originals clazz.__old_init = clazz.__init__ clazz.__old_save = clazz.save # Override (and add helper) clazz.__init__ = __init__ clazz.__get_state_helper = __get_state_helper clazz.save = save return clazz return fx </code></pre> <p>And use it as follows (only relevant part):</p> <pre><code>@audit_fields(["status"], fx) class Order(models.Model): BASKET = "BASKET" OPEN = "OPEN" PAID = "PAID" SHIPPED = "SHIPPED" CANCELED = "CANCELED" ORDER_STATES = ( (BASKET, 'BASKET'), (OPEN, 'OPEN'), (PAID, 'PAID'), (SHIPPED, 'SHIPPED'), (CANCELED, 'CANCELED') ) status = models.CharField(max_length=16, choices=ORDER_STATES, default=BASKET) </code></pre> <p>And test on the Django shell with:</p> <pre><code>from store.models import Order o=Order() o.status=Order.OPEN o.save() </code></pre> <p>The error I receive then is:</p> <pre><code>TypeError: int() argument must be a string or a number, not 'Order' </code></pre> <p>The full stacktrace is here: <a href="https://gist.github.com/4020212" rel="nofollow">https://gist.github.com/4020212</a></p> <p>Thanks in advance and let me know if you would need more info!</p> <p><strong>EDIT:</strong> Question answered by randomhuman, code edited and usable as shown!</p>

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