How to Pickle Django Model

Question

I'm currently trying to pickle certain Django models. I created a __getstate__ and __setstate__ method for the model, but it looks like pickle.dumps() is using the default __reduce__ instead.

Is there a way to force use of __getstate__ and __setstate__ ? If not, what is the best way to overwrite __reduce__ ?

I am currently using Django 1.6 and Python 2.7.6, if that helps.

In essence, I am using get and set state to remove two fields before pickling in order to save space.

Answer 1

While it's not really the "answer" to my question, the best solution I found was to implement a dehydrate() method on the model, allowing me to alter the model's __dict__ and store that instead.

On recovery from the cache, it's as simple as using the ** syntax and you'll have your original model back.

Answer 2

Using pickle getstate/setstate you can have your models automatically pickle just the primary key and use it to load when unpickle.

https://docs.python.org/2/library/pickle.html#object. getstate

Like so:

class FooModel(Model):
    field1 = CharField()

    def __getstate__(self):
        return self.pk

    def __setstate__(self, state):
        self.pk = state
        self.refresh_from_db()

This let's you pickle django models and all it stores is the primary key. Then when you unpickle it it does a fetch for the fields using the primary key.