How to delete nested session data in Django?

Question

I set data to session with 'cart' key:

request.session['cart'] = {'8': ['a', 'b'], '9': ['c', 'd']}

Then, I could delete all the session data with 'cart' key:

del request.session['cart']

But, I could not delete ['a', 'b'] with '8' key:

del request.session['cart']['8']

So, how can I delete ['a', 'b'] with '8' key?

Answer 1

The django session object can only save when its modified. But because you are modifying an object within session, the session object doesn't know its being modified and hence it cant save.

To let the session object know its modified use:

request.session.modified = True

From the django docs :

https://docs.djangoproject.com/en/dev/topics/http/sessions/

When sessions are saved By default, Django only saves to the session database when the session has been modified – that is if any of its dictionary values have been assigned or deleted:

# Session is modified. 
request.session['foo'] = 'bar'

# Session is modified. 
del request.session['foo']

# Session is modified. 
request.session['foo'] = {}

# Gotcha: Session is NOT modified, because this alters
# request.session['foo'] instead of request.session.
request.session['foo']['bar'] = 'baz' 

In the last case of the above example, we can tell the session object explicitly that it has been modified by setting the modified attribute on the session object:

  request.session.modified = True

To change this default behavior, set the SESSION_SAVE_EVERY_REQUEST setting to True. When set to True, Django will save the session to the database on every single request.

Note that the session cookie is only sent when a session has been created or modified. If SESSION_SAVE_EVERY_REQUEST is True, the session cookie will be sent on every request.

Similarly, the expires part of a session cookie is updated each time the session cookie is sent.

The session is not saved if the response’s status code is 500.