Active Record Querying-Help

I am new to rails and stuck on one Querying issue. Here is the
situation.

Model: Category
class Category < ActiveRecord::Base
  has_and_belongs_to_many :postings
  has_and_belongs_to_many :volunteers
end

Model: Posting
class Posting < ActiveRecord::Base
  has_and_belongs_to_many :categories
end

Model: Volunteer
class Volunteer < ActiveRecord::Base
  has_and_belongs_to_many :categories
end

Is that not the same problem you posted a few days ago, and then
posted the solution?

Colin