mongoid/mongoid — pull request #1387 by seivan (2011-10-30 18:37:26+00:00)
Title: added cache_key  - this is being called in cache blocks as a convienience.

By using updated_at, it ensures that only new views are cached, and memcached can pop out older views.

I need this for my fragment caching as I use both AR(SQL) and Mongoid. And I want to have the same convention for fragment caching the views.
By passing in the model objects.

```ruby
cache [@user, @profile, "sidebar] do
#Some code
end
```
Also I wrote the specs pass under timestamp.

Not sure about where the particular code and specs should reside so I put them under timestamp.
Naturally this might not be the best case, but hopefully it's good enough as a starting point to raise the feature request.