Add "pending_column" for performance when checking if pending moderation

[swiharta]

I'm working out how to add a "pending_column" to improve performance when you want to check which of a large number of moderated model instances are pending moderation. I added a 'pending' Boolean field to my model and referenced it as my 'pending_column' when I subclassed moderator.GenericModerator.

As a first step, in register.py pre_save_handler I added:

if moderator.pending_column:
    setattr(instance, moderator.pending_column, True)

After saving a change to a model instance, on viewing this instance in the admin, I can see the 'pending' attribute appropriately set as True, but when I do mymodel_instance.pending, it strangely returns False. I'm not sure what's going on here, likely something to do with the manager, any idea?

[treyhunner]

The pending attribute is probably being set on the unapproved version of the object stored in the changed_object field of ModeratedObject and not in the original instance.

[swiharta]

Actually, I just replaced instance with moderated_obj.changed_object, and while it seems kind of hacky, it produces exactly the behavior I want. I guess changed_object in this case represents a copy of the original model instance, and this is what the objects manager retrieves if a ModeratedObject exists, rather than the instance itself? The variable name is a little confusing, because this "changed object" is actually supposed to be a copy of the unchanged model instance, if I'm getting this right.

In register.py pre_save_handler, I added:

if moderator.pending_column: # is 'pending_column' in your subclassed GenericModerator
    setattr(moderated_obj.changed_object, moderator.pending_column, True) # set 'pending_column' True in the visible instance
moderated_obj.save()

'pending' becomes False after I approve a change, automatically it seems, because the True was only applied to a copy of the original instance, not the instance itself, at least that's how it seems to be occurring.

Now I can do model_instance.pending in my templates / view to see if there is a pending change under moderation, without generating extra db queries. Seems to be working as intended so far, I'll report back with any problems.

EDIT: Still work to do, this isn't working consistently.

[dominno]

@swiharta so how you would named changed_object to be more descriptive ? I named it changed because it holds changed version of original object that is available on live.

Why you need this pending column ? what are you trying to do ?

[swiharta]

I "want to check which of a large number of moderated model instances are pending moderation".

I have a calendar app populated with events. I want to have all the events under moderation, and basically I just want to add a CSS class "moderating" to each event on the calendar if there is a pending change (if the corresponding ModeratedObject status is "pending"). In a private message here on GitHub you and I discussed how to do this without a "pending column", but it generated an extra query for each event, so this column would improve performance, that's the point.

As far as the "changed_object" nomenclature, I think its fine if it is what you say it is, it's just that in my limited testing, as above, it seemed like the "changed_object" was actually an "unchanged_object". I need to dig in deeper to understand what's going on, there is a lot of passing around versions of objects and I'm a noob.