[ckan-dev] followers and thoughts

[Sean Hammond]

> I've had a look at the followers stuff following a bug I found, and looking
> to add it to the demo site.
> 
> I'd like to move the logic from the controllers into a helper function.
> The reason for this is that it means that we don't need to do the work
> finding followers if the feature isn't being used in a particular ckan
> instance.  It also decouples it from the controllers so it would be
> available even with a customised controller.
> 
> essentially I'd remove the follower stuff from the controllers and get the
> helper function to do the work.  All the logic work would remain the same.
> It isn't yet in a released version of ckan so no-one should be affected.
> 
> so we'd end up with something close to h.follow_button('dataset', pkg_id),
> h.follow_numbers('user', user_name)

Yes! This seems like a good idea to me. Just so everyone's on the same
page, I think the only logic on the controllers you're talking about is
that they call *_follower_list() and *_follower_count() action functions
and save the results in the context for the templates to retrieve. This
was one of the biggest pain points implementing follower because I had
to do this in each controller method that needs it: in read(), authz(),
resource_read() and history() in the package controller, a few places in
the user controller, and also in the new related controller. Of course
you can make a private helper method in the controller class to do it
but you still have to make sure each controller method that needs it
calls that helper method. So having to write it just once in a helper
function sounds much better, and will also mean that the action
functions aren't called unless the template actually uses them.

A couple of thoughts I had about it, what if the same template calls the
same helper multiple times with the same args? Would make unnecessary
database accesses. The helper function could do some caching perhaps,
e.g. against the pylons context, to avoid this. Not likely to happen
with follower or activity streams anyway.

Would the helper function be much more than a boilerplate wrapper for
the action function? What about just calling the action API from to
templates? I guess the helper function will also handle wrapping the API
output in the <button> HTML, etc.

> part of the reason for this is situations like the ckan index page building
> the recent activity stream but not then displaying it. So all ckan
> instances end up taking a hit because of the needs of a few instances. I'd
> like to slowly move such things out of the controllers where
> possible/appropriate.

Yes, this seems like a good idea to me, lets us throw in new 'extra'
features like follower and activity streams without slowing down page
loads if you're not using them.

This is the kind of thing that I think we should be writing about in the
coding standards. Sure we should link to general stuff like PEP 8 and
the Google Python Style Guide etc., but even more useful will be
specific things about the right way to do things in CKAN.