Allow reverting of migration commands with Migration#revert [#8267]

activerecord/lib/active_record/migration.rb

@@ -373,22 +373,52 @@ def initialize(name = self.class.name, version = nil)
       @name       = name
       @version    = version
       @connection = nil
-      @reverting  = false
     end
 
     # instantiate the delegate object after initialize is defined
     self.verbose  = true
     self.delegate = new
 
+    # Reverses the migration commands for the given block.
+    #
+    # The following migration will remove the table 'horses'
+    # and create the table 'apples' on the way up, and the reverse
+    # on the way down.
+    #
+    #   class FixTLMigration < ActiveRecord::Migration
+    #     def change
+    #       revert do
+    #         create_table(:horses) do |t|
+    #           t.text :content
+    #           t.datetime :remind_at
+    #         end
+    #       end
+    #       create_table(:apples) do |t|
+    #         t.string :variety
+    #       end
+    #     end
+    #   end
+    #
+    # This command can be nested.
+    #
     def revert
-      @reverting = true
-      yield
-    ensure
-      @reverting = false
+        if @connection.respond_to? :revert
+          @connection.revert { yield }
+        else
+          recorder = CommandRecorder.new(@connection)
+          @connection = recorder
+          suppress_messages do
+            @connection.revert { yield }
+          end
+          @connection = recorder.delegate
+          recorder.commands.each do |cmd, args, block|
+            send(cmd, *args, &block)
+          end
+        end
     end
 
     def reverting?
-      @reverting
+      @connection.respond_to?(:reverting) && @connection.reverting
     end
 
     def up
@@ -414,29 +444,19 @@ def migrate(direction)
 
       time   = nil
       ActiveRecord::Base.connection_pool.with_connection do |conn|
-        @connection = conn
-        if respond_to?(:change)
-          if direction == :down
-            recorder = CommandRecorder.new(@connection)
-            suppress_messages do
-              @connection = recorder
+        time = Benchmark.measure do
+          @connection = conn
+          if respond_to?(:change)
+            if direction == :down
+              revert { change }
+            else
               change
             end
-            @connection = conn
-            time = Benchmark.measure {
-              self.revert {
-                recorder.inverse.each do |cmd, args|
-                  send(cmd, *args)
-                end
-              }
-            }
           else
-            time = Benchmark.measure { change }
+            send(direction)
           end
-        else
-          time = Benchmark.measure { send(direction) }
+          @connection = nil
         end
-        @connection = nil
       end
 
       case direction
@@ -483,7 +503,7 @@ def method_missing(method, *arguments, &block)
       arg_list = arguments.map{ |a| a.inspect } * ', '
 
       say_with_time "#{method}(#{arg_list})" do
-        unless reverting?
+        unless @connection.respond_to? :revert
           unless arguments.empty? || method == :execute
             arguments[0] = Migrator.proper_table_name(arguments.first)
             arguments[1] = Migrator.proper_table_name(arguments.second) if method == :rename_table

activerecord/lib/active_record/migration/command_recorder.rb

@@ -16,35 +16,54 @@ class Migration
     class CommandRecorder
       include JoinTable
 
-      attr_accessor :commands, :delegate
+      attr_accessor :commands, :delegate, :reverting
 
       def initialize(delegate = nil)
         @commands = []
         @delegate = delegate
+        @reverting = false
+      end
+
+      # While executing the given block, the recorded will be in reverting mode.
+      # All commands recorded will end up being recorded reverted
+      # and in reverse order.
+      # For example:
+      #
+      #   recorder.revert{ recorder.record(:rename_table, [:old, :new]) }
+      #   # same effect as recorder.record(:rename_table, [:new, :old])
+      def revert
+        @reverting = !@reverting
+        previous = @commands
+        @commands = []
+        yield
+      ensure
+        @commands = previous.concat(@commands.reverse)
+        @reverting = !@reverting
       end
 
       # record +command+. +command+ should be a method name and arguments.
       # For example:
       #
       #   recorder.record(:method_name, [:arg1, :arg2])
-      def record(*command)
-        @commands << command
+      def record(*command, &block)
+        if @reverting
+          @commands << inverse_of(*command, &block)
+        else
+          @commands << (command << block)
+        end
       end
 
-      # Returns a list that represents commands that are the inverse of the
-      # commands stored in +commands+. For example:
+      # Returns the inverse of the given command. For example:
       #
-      #   recorder.record(:rename_table, [:old, :new])
-      #   recorder.inverse # => [:rename_table, [:new, :old]]
+      #   recorder.inverse_of(:rename_table, [:old, :new])
+      #   # => [:rename_table, [:new, :old]]
       #
       # This method will raise an +IrreversibleMigration+ exception if it cannot
-      # invert the +commands+.
-      def inverse
-        @commands.reverse.map { |name, args|
-          method = :"invert_#{name}"
-          raise IrreversibleMigration unless respond_to?(method, true)
-          send(method, args)
-        }
+      # invert the +command+.
+      def inverse_of(command, args, &block)
+        method = :"invert_#{command}"
+        raise IrreversibleMigration unless respond_to?(method, true)
+        send(method, args, &block)
       end
 
       def respond_to?(*args) # :nodoc:
@@ -56,9 +75,9 @@ def respond_to?(*args) # :nodoc:
         :change_column, :change_column_default, :add_reference, :remove_reference,
       ].each do |method|
         class_eval <<-EOV, __FILE__, __LINE__ + 1
-          def #{method}(*args)          # def create_table(*args)
-            record(:"#{method}", args)  #   record(:create_table, args)
-          end                           # end
+          def #{method}(*args, &block)          # def create_table(*args, &block)
+            record(:"#{method}", args, &block)  #   record(:create_table, args, &block)
+          end                                   # end
         EOV
       end
       alias :add_belongs_to :add_reference

activerecord/test/cases/invertible_migration_test.rb

@@ -17,6 +17,17 @@ def change
       end
     end
 
+    class InvertibleRevertMigration < SilentMigration
+      def change
+        revert do
+          create_table("horses") do |t|
+            t.column :content, :text
+            t.column :remind_at, :datetime
+          end
+        end
+      end
+    end
+
     class NonInvertibleMigration < SilentMigration
       def change
         create_table("horses") do |t|
@@ -67,6 +78,18 @@ def test_migrate_down
       assert !migration.connection.table_exists?("horses")
     end
 
+    def test_migrate_revert
+      migration = InvertibleMigration.new
+      revert = InvertibleRevertMigration.new
+      migration.migrate :up
+      revert.migrate :up
+      assert !migration.connection.table_exists?("horses")
+      revert.migrate :down
+      assert migration.connection.table_exists?("horses")
+      migration.migrate :down
+      assert !migration.connection.table_exists?("horses")
+    end
+
     def test_legacy_up
       LegacyMigration.migrate :up
       assert ActiveRecord::Base.connection.table_exists?("horses"), "horses should exist"