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.

Answer 2

@user.role_extensions.where(:joins => :roles)

Answer 3

Normally you'd use a has_many, :through association, but that doesn't apply to has_and_belongs_to_many relations.

So, instead, in your User model:

def role_extensions
  return roles.inject([]) do |array, role|
    role.role_extensions do |re|
      array.include?(re) ? array << re : array
    end
  end
end

Then my_user.role_extensions should return an array of all role extensions belonging to all the user's roles.

Note: I haven't tested this, but it should work

UPDATE: I like this better

def role_extensions
  return roles.inject([]) { |array, role| array << role.role_extensions }.flatten!.uniq
end

Answer 4

Try this -

# Fetch user object
user = User.first

# If you want roles of that user try this
roles = user.roles

# You can map all the role extensions of that user by
role_extensions = user.roles.map(&:role_extensions).uniq

Be aware that this will be extremely slow for large number of roles. In that case better write your own query method. Something like

role_extensions = RoleExtension.where("role_id in (?)", user.role_ids).all