use_session_state hook #32

Old Behavior

State is generated on a per-render basis and has no method of being permanently stored.

New Behavior

Allow for persistent state that is databased backed, linked to a user's Session.

This will only function when django.contrib.sessions is in INSTALLED_APPS

Implementation Details

Persistently store/restore state within a database model, linked to a Session as a foreign key.

Store context data within a BinaryField.

This will require only serializable data to be used within this. Consider using dill.pickle to serialize data more robustly than standard library.

The state should only be fetched from the database once, upon first initialization of the hook's state value. On every set_state call, the value should be synchronized to the database.

We may want to document that the user should regularly purge old sessions.

This implementation will require the use of database-backed sessions or django.contrib.sessions.backends.cached_db.

Example Database Model

class IdomSessionState(models.Model):
    # One state is stored per user browser session
    # When the browser session expires, the state is deleted from the database
    session = models.ForeignKey(Session, on_delete=models.CASCADE)
    state = models.BinaryField(blank=True, null=True)

The interface may look like this...

# Note: The default state is only used in situations where there is no value in the database
# The websocket is needed in order to grab the session from the `scope`
state, set_state = hooks.use_session_state({"foo":"bar"}, websocket=websocket)
print(state.data)

# This saves the values to the database
set_state({"something":"else"})

In the background, the set state is doing the following...

def set_state(state, websocket):
    query = IdomSessionState.objects.get_or_create(session=websocket.scope.user.session)
    query.state = dill.pickle(state)
    query.save()
    ...

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