#407 Activity Feed from Scratch pro

Ryan, it looks like in the second half of the episode you were really after ActiveRecord's to_partial_path, which you can define in Activity model and have it perform all of your path-building logic. It becomes a clear winner when you notice that

"activities/#{activity.trackable_type.underscore}/#{activity.action}"

becomes

"activities/#{trackable_type.underscore}/#{action}"

Makes more sense to have it come from inside the activity object itself. In the view you could then simply call render activity, and it would automatically call to_partial_path on the model. When this logic is moved into model like that, presenter is left somewhat empty, and in this specific case becomes excessive.

By using a service object you could wrap the save of recipe (e.g.) and the creation of feed in a transaction. Otherwise you could have an activity succeed without its companion feed row being created.

I don't see why you keep saying that you cannot get the user reference in the model. On create the activity owner would be the creator referenced in the recipe/comment. If other users can update these, you would likely store the last modifier in the database for later reference anyway, so you can also reference them in the callback.

For me, this functionality does belong in a callback and nowhere else, precisely because it is possible that there are other ways, these items can be created. Things like combining/filtering/spam protection would also have to be implemented when you create activities in the controller at some point of professionalization of an app. So this is no argument against callbacks.

Great episode. On quick question though. I would've thought that the presenter in this case would be 'just' a helper. Why did you make it a presenter? Thanks!

Have you thought about doing this with redis as demonstrated by obie here? - http://www.youtube.com/watch?v=dH6VYRMRQFw

I implemented an activity feed last year which was a bit more complex than this. It had to store data such as specific actions like updating a models state column (from/to), as well as displaying consecutive activity grouped by the person who did it, and grouping the same consecutive action by the same person as "XX updated XXX (4 times)". Would be nice to see another pro episode that handled this display related stuff, since my code is kind of messy, and it's be cool to see how it might be implemented by someone else.

I am not quite familiar with the concept of Presenters. Can you recommend any articles/videos on the topic?

This tutorial was very helpful for me! Few weeks ago I've been working on activity feed myself. Any ideas how to aggregate activities to look something like 'Mike followed Ryan and 6 other developers'? Also my trackable object are polymorphic as well. Comment belongs to commentable models, Follow belongs to followable models. So it would be great to show follows and comments based on their polymorphic parent models. Is there any good solution? Thanks!

Displaying activity items generates a lot of sql queries, especially N+1 queries. Is there a way to get around this?

commented on <%= link_to activity.trackable.recipe.name, activity.trackable.recipe %>

For this code, How come I get error undefined method, I'm not using the exact names for my values, I'm doing it this way,

commented on <%= link_to activity.trackable.list.name, activity.trackable %>

but I'm not sure why I don't have to add a .list at the end of my code? Instead I can just stop at .trackable

-1 for the Presenters.