activerecord/lib/active_record/migration/command_recorder.rb


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module ActiveRecord
  class Migration
    # ActiveRecord::Migration::CommandRecorder records commands done during
    # a migration and knows how to reverse those commands.
    class CommandRecorder
      attr_reader :commands

      def initialize
        @commands = []
      end

      # record +command+.  +command+ should be a method name and arguments.
      # For example:
      #
      #   recorder.record(:method_name, [:arg1, arg2])
      def record(*command)
        @commands << command
      end

      # Returns a list that represents commands that are the inverse of the
      # commands stored in +commands+.
      def inverse
        @commands.map { |name, args| send(:"invert_#{name}", args) }
      end

      private
      def invert_create_table(args)
        [:drop_table, args]
      end

      def invert_rename_table(args)
        [:rename_table, args.reverse]
      end

      def invert_add_column(args)
        [:remove_column, args.first(2)]
      end

      def invert_rename_index(args)
        [:rename_index, args.reverse]
      end

      def invert_rename_column(args)
        [:rename_column, [args.first] + args.last(2).reverse]
      end
    end
  end
end