A Little Helper To Help You :through

Do you have to code a lot of "has_many :through" relation models in your Rails application? Here is a little helper that will help you DRY. It is very simple indeed, for an example here are the models:
Party, ContectMech and PartyContectMech(the join model).

Call many_to_many_through, perhaps in your application.rb

# many_to_many_through PartyContectMech, Party, ContectMech returns:
#    Party.has_many :party_contact_meches, :foreign_key => :party_id
#    Party.has_many :contact_meches, :through => :party_contact_meches, :foreign_key => :party_id
#
#    ContactMech.has_many :party_contact_meches, :foreign_key => :contact_mech_id
#    ContactMech.has_many :parties, :through => :party_contact_meches, :foreign_key => :contact_mech_id
#
#    PartyContactMech.belongs_to :party
#    PartyContactMech.belongs_to :contact_mech
#
# evaluating the result defines the necessary 6 relations,
# * save some typing, 
# * no need to jump between the 3 source files,
# * less chance for typo and/or human mistake
  eval many_to_many_through(PartyContectMech, Party, ContectMech)



SOURCE:

  def many_to_many_through(through_model, model1, model2)
    through_table = through_model.table_name
    table1 = model1.table_name
    table2 = model2.table_name
    model1_id = model1.name.underscore + "_id"
    model2_id = model2.name.underscore + "_id"
%Q{
    #{model1}.has_many :#{through_table}, :foreign_key => :#{model1_id}
    #{model1}.has_many :#{table2}, :through => :#{through_table}, :foreign_key => :#{model1_id}

    #{model2}.has_many :#{through_table}, :foreign_key => :#{model2_id}
    #{model2}.has_many :#{table1}, :through => :#{through_table}, :foreign_key => :#{model2_id}

    #{through_model}.belongs_to :#{model1.name.underscore}
    #{through_model}.belongs_to :#{model2.name.underscore}
}
  end