has_and_belongs_to_many_association.rb

module ActiveRecord
  # = Active Record Has And Belongs To Many Association
  module Associations
    class HasAndBelongsToManyAssociation < CollectionAssociation #:nodoc:
      attr_reader :join_table

      def initialize(owner, reflection)
        @join_table = Arel::Table.new(reflection.join_table)
        super
      end

      def insert_record(record, validate = true, raise = false)
        if record.new_record?
          if raise
            record.save!(:validate => validate)
          else
            return unless record.save(:validate => validate)
          end
        end

        stmt = join_table.compile_insert(
          join_table[reflection.foreign_key]             => owner.id,
          join_table[reflection.association_foreign_key] => record.id
        )

        owner.class.connection.insert stmt

        record
      end

      private

        def count_records
          load_target.size
        end

        def delete_records(records, method)
          relation  = join_table
          condition = relation[reflection.foreign_key].eq(owner.id)

          unless records == :all
            condition = condition.and(
              relation[reflection.association_foreign_key]
                .in(records.map { |x| x.id }.compact)
            )
          end

          owner.class.connection.delete(relation.where(condition).compile_delete)
        end

        def invertible_for?(record)
          false
        end
    end
  end
end