This definition supposes a relational data store. The active record pattern would not apply to document oriented systems such as CouchDB, Mongo, and other No-SQL databases, as they tend to store aggregates.
I rarely use these options. :select can lead to confusion if you select columns from more than one table because the returned objects will be read-only. I have yet to find a common use case for :group
Many times complex views will want to be backed by a custom finder to avoid N+1 issues. I usually place these in a finder module mixed into my model class to keep the model class clean.
This is where we begin joining models to other models to reflect the domain space.
I very rarely use this type of association. I find that my join models eventually begin to a
To halt the chain return false. To continue return true.
Intro to Rails ActiveRecord
Introduction to ActiveRecord <ul><li>The Rails Object Relational Mapper </li></ul><ul><li>by Mark Menard, Vita Rara, Inc. </li></ul>