We had seen how a has_and_belongs_to_many works with a join table. But apart from carrying the foreign keys the join table has nothing much to do over there. So to have more features added and retaining the goal of having many-to-many relationships we will discuss now another rails offering "has_many, :through".
The above snippet shows a simple example from Josh Susser's blog.
The scenario shows that there are two tables "books" and "contributors" and the a join table "contributions". This is entirely different from habtm, where we had the join table with combination of tables.
And syntactically, we say to each of tables (books, contributors) that they are related to each other through "contributions".
So the join table would have a simple belongs_to and the individual tables will be related with has_many:'table_name' and keyword :through=>'name_of_join_table'
That is with the ActiveRecord relationships. Just to recap
has_many, has_one, belongs_to
We will be slowly moving into other part of rails packages, ActionPack soon.