module DeveloperProjectsAssociationExtension def find_most_recent find(:first, :order => "id DESC") end end module DeveloperProjectsAssociationExtension2 def find_least_recent find(:first, :order => "id ASC") end end class Developer < ActiveRecord::Base has_and_belongs_to_many :projects do def find_most_recent find(:first, :order => "id DESC") end end has_and_belongs_to_many :projects_extended_by_name, :class_name => "Project", :join_table => "developers_projects", :association_foreign_key => "project_id", :extend => DeveloperProjectsAssociationExtension has_and_belongs_to_many :projects_extended_by_name_twice, :class_name => "Project", :join_table => "developers_projects", :association_foreign_key => "project_id", :extend => [DeveloperProjectsAssociationExtension, DeveloperProjectsAssociationExtension2] has_and_belongs_to_many :special_projects, :join_table => 'developers_projects', :association_foreign_key => 'project_id' validates_inclusion_of :salary, :in => 50000..200000 validates_length_of :name, :within => 3..20 end DeveloperSalary = Struct.new(:amount) class DeveloperWithAggregate < ActiveRecord::Base self.table_name = 'developers' composed_of :salary, :class_name => 'DeveloperSalary', :mapping => [%w(salary amount)] end class DeveloperWithBeforeDestroyRaise < ActiveRecord::Base self.table_name = 'developers' has_and_belongs_to_many :projects, :join_table => 'developers_projects', :foreign_key => 'developer_id' before_destroy :raise_if_projects_empty! def raise_if_projects_empty! raise if projects.empty? end end