Django不可变模型查询

Question

I'm looking at a state isolation / read-only situation in Django (1.6) and i'm looking for a method to make a query return objects that are immutable.

I'm looking to fit something like the following wrapping the usual db atomicity api

MyModel.objects.filter(foo="bar").all(read_only=True)

My current thinking is this will be a custom Manager, but i'd potentially like something that can be added at runtime like:

read_only(MyModel.objects.filter(foo="bar").all())

Without too much voodoo or making them unmanaged (the option to throw an Exception on state change would be good).

The key thing is that the Model supports both read-only and the default read-write query type ideally with changes limited to code that is required to be read-only.

My other option is something like:

with isolation(raise_exception=True):
    m = MyModel.objects.get(id=foo)
    m.do_unknown_thing_that_may_mutate()

Are there existing solutions I'm missing at a higher level than the database?

Answer 1

One possibility might be to define a proxy class which overrides save to be a no-op:

class MyReadOnlyModel(MyModel):
    def save(self, *args, **kwargs):
        pass
    class Meta:
        proxy = True

Then just query MyReadOnlyModel instead of MyModel.