through_model

# File activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb, line 13
    def through_model
      join_model = Class.new(ActiveRecord::Base) {
        class << self
          attr_accessor :left_model
          attr_accessor :name
          attr_accessor :table_name_resolver
          attr_accessor :left_reflection
          attr_accessor :right_reflection
        end

        def self.table_name
          # Table name needs to be resolved lazily
          # because RHS class might not have been loaded
          @table_name ||= table_name_resolver.call
        end

        def self.compute_type(class_name)
          left_model.compute_type class_name
        end

        def self.add_left_association(name, options)
          belongs_to name, required: false, **options
          self.left_reflection = _reflect_on_association(name)
        end

        def self.add_right_association(name, options)
          rhs_name = name.to_s.singularize.to_sym
          belongs_to rhs_name, required: false, **options
          self.right_reflection = _reflect_on_association(rhs_name)
        end

        def self.retrieve_connection
          left_model.retrieve_connection
        end

        private
          def self.suppress_composite_primary_key(pk)
            pk unless pk.is_a?(Array)
          end
      }

      join_model.name                = "HABTM_#{association_name.to_s.camelize}"
      join_model.table_name_resolver = -> { table_name }
      join_model.left_model          = lhs_model

      join_model.add_left_association :left_side, anonymous_class: lhs_model
      join_model.add_right_association association_name, belongs_to_options(options)
      join_model
    end