Django QuerySet-如何“禁用”先前的过滤值

Question

I have a base model class that creates history of an object each time the objects has been changed. The model has field named 'is_history'. The idea is that a new instance of the model is created with the old data each time the model has been changed by someone. The new model with the old data has 'is_history=True' because becomes history object. In the default admin changelist I do not want to see the history objects. I do not want to see them anywhere by default. Thats why i created new manager that overwrites the default get_query_set() and adds 'is_history=False'.

def get_query_set(self):
    qs = super(ModelHistoryManager, self).get_query_set()
    return qs.filter(is_history=False)

But I also should be able to show the history objects in the changelist view rarely, using admin filter for example.

My question is: I have a queryset that has already filtered this value. But in the admin's filter I get the filtered queryset from the base manager and I want to change this filter from is_history=False to is_history=True, or to remove the filter for 'is_history' if the user wants to show all records - both history and original records.

Any idea?

Answer 1

Let me quote the django Docs about Custom Managers :

If you use custom Manager objects, take note that the first Manager Django encounters (in the order in which they're defined in the model) has a special status. Django interprets the first Manager defined in a class as the “default” Manager, and several parts of Django (including dumpdata) will use that Manager exclusively for that model. As a result, it's a good idea to be careful in your choice of default manager in order to avoid a situation where overriding get_query_set() results in an inability to retrieve objects you'd like to work with.

So, you should do something like:

class MyModel(Model):
    objects = models.Manager() # The default manager.
    custom_manager = MyCustomManager() # This has overrided the get_query_set method

Of course, you should use custom_manager instead of objects if you want the filtered model instances

Answer 2

You can hack it , but let me warn you that, this is a very bad idea and touches internals not meant to be touched by users. But if you insist, this would do the trick:

from django.db.models.sql.where import WhereNode
qs.query.where = WhereNode()