Could I add an association based on another association?

Question

My User model looks like:

User
   habtm  :Roles


Role
   habtm  :Users


RoleExtension
   belongs_to  :Role

mysql tables:

Answer 1

user = User.find(1)
RoleExtension.find(:all, :conditions => ["role_id IN (?)", user.role_ids])

Otherwise you can use nested joins.