Implementing a user activity log with STI. (?)

Can anyone tell me if I’m on the right track? I think this isn’t
quite right:

I want to implement an activity log for users. It’ll show them a list
of the objects they’ve viewed. I have, of course, many types of
objects in the Rails program.

I’ve thought that I’d make a log_entries table which would have
a :viewed_object_id and :viewed_object_type.

I’d then like to be able to retrieve all of the viewed objects,
something along the lines:{|e| e.viewed_object}

And I could display links to them, like:

link_to obj.to_s, obj

…so, this is a form of STI, but I’m not sure if Rails handles this
kind. I’m also not sure if this is the best way to implement this
kind of feature.

Thanks for any feedback!

Hi Robb,

I ended up writing a very crude solution and then stopped that to
revamp later. I DO believe you are on the right track though. The only
part that I havent figured out though is writing neat code for the
actual message or sentence the user will read. Like,

You edited the task - Change tyres on car
Robb completed the task - Change tyres on car

These sentences will vary depending on the action, object and user. To
generate them using a function is, at least in my case, not possible.
Im hard coding them right now.

Read up on polymorphic relationships. Its basically what you have
suggested above, only, Rails makes it a bit easier.

Good luck!
And DO update this post with your efforts.

Thanks, Ram. Yep, I realized that polymorphic associations is exactly
what I was talking about. In my case, all the log info is private and
per-user. Also, the only action is “view”, so I have a simpler case
than you. I just need to generate a list like,

Document 452.242
Document 551.432

Document 43.234
Chapter 452

Now, in your case, I wouldn’t worry at all about how to generate the
text. This is an issue for the presentation layer. I’d just be
concerned with making sure I have all the relevant objects so that the
various templates can render the output appropriately: the currently
logged in user, a list of log entries, each of which has a reference
to the relevant object, the method invoked, and the user who did it.

I suggest checking out the “Command” design pattern. It kind of
sounds like what you’re doing.

  • Robb

On Aug 12, 9:29 pm, Ram [email protected] wrote:

… The only
part that I havent figured out though is writing neat code for the
actual message or sentence the user will read. Like,

Nice. Went through a wiki article on Command Pattern. Very much the
design i need. Will try to do that when I get back to the activity
log :).

you guyes are doing what I want to implement soon. So I had some
thoughts about an activity log. Pretty sure polymorphic associations
are a good choice. To keep the rest clean from logging code and the
logging flexible, I thought about using an observer, like

class ActivityObserver < ActiveRecord::Observer
observe :model_2_observe_01, model_2_observe_2 #, …

def after_save(record)
activity =

Should do it. I just wonder if Rails ensures ACID behavoir for
observers, anyone knows?


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