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Memcached, Rails, and You

Geoffrey continues the run of helpful articles with an intro of how to implement memcached with ActiveRecord. I know my team will have to look into this soon, as we have some model objects that are essentially lookup objects, but need to be used for every request in some way. Since they change rarely, we should just be able to load them once a day and let them sit in memory.

Robot Coop’s cached-model looks like it would help for this, but I don’t understand why its implemented as a class instead of a module? Seems like caching should be an implementation detail, so a module would be perfect. Once you use cached-model you are stuck with that inheritance, and now you have to hack your way around it if you want to use some sort of common abstract class. I feel the same way about the using a base class like “AlternateDatabase” to enable multiple database connectivity, but sometimes quick and easy wins out over the “right way”

I agree with you on both these points. Where I work, we have all our models inherit from ActiveRecord::Base and that’s that. For the multi-db problem, we’ve rolled a plugin we call named_connections (”uses_connection :user_db” in all the models which use the user db, for instance). For memcached we’ve rolled our own acts_as_cached plugin which I will be giving a presentation on (as well as other memcached tips) at the September San Francisco Ruby meetup. My main problem with CachedModel, aside from forcing you to inherit, is that it only allows you to cache single, non-associated ActiveRecord objects. We’ve felt the need to do more (without repeating code over and over) and acts_as_cached addresses this. Maybe you can have a look when it’s out? I’d love feedback.

That sounds great, Chris. I’d love to take a look at it, and may integrate it into our stuff once its available. I’ll be watching your feed for an announcement on it.

Here’s why we use subclassing instead of include for CachedModel.