Add rake db:forward - opposite of db:rollback [#768 state:resolved]

Example:
  rake db:forward # performs the next migration
  rake db:forward STEP=4 # performs the next 4 migrations

Signed-off-by: Pratik Naik <pratiknaik@gmail.com>

activerecord/lib/active_record/migration.rb

@@ -397,6 +397,16 @@ def rollback(migrations_path, steps=1)
         down(migrations_path, finish ? finish.version : 0)
       end
 
+      def forward(migrations_path, steps=1)
+        migrator = self.new(:up, migrations_path)
+        start_index = migrator.migrations.index(migrator.current_migration)
+
+        return unless start_index
+
+        finish = migrator.migrations[start_index + steps]
+        up(migrations_path, finish ? finish.version : 0)
+      end
+
       def up(migrations_path, target_version = nil)
         self.new(:up, migrations_path, target_version).migrate
       end

activerecord/test/cases/migration_test.rb

@@ -1136,6 +1136,17 @@ def test_migrator_rollback
       assert_equal(0, ActiveRecord::Migrator.current_version)
     end
 
+    def test_migrator_forward
+      ActiveRecord::Migrator.migrate(MIGRATIONS_ROOT + "/valid", 1)
+      assert_equal(1, ActiveRecord::Migrator.current_version)
+
+      ActiveRecord::Migrator.forward(MIGRATIONS_ROOT + "/valid", 2)
+      assert_equal(3, ActiveRecord::Migrator.current_version)
+
+      ActiveRecord::Migrator.forward(MIGRATIONS_ROOT + "/valid")
+      assert_equal(3, ActiveRecord::Migrator.current_version)
+    end
+
     def test_schema_migrations_table_name
       ActiveRecord::Base.table_name_prefix = "prefix_"
       ActiveRecord::Base.table_name_suffix = "_suffix"

railties/lib/tasks/databases.rake

@@ -172,6 +172,13 @@ namespace :db do
     Rake::Task["db:schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
   end
 
+  desc 'Pushes the schema to the next version. Specify the number of steps with STEP=n'
+  task :forward => :environment do
+    step = ENV['STEP'] ? ENV['STEP'].to_i : 1
+    ActiveRecord::Migrator.forward('db/migrate/', step)
+    Rake::Task["db:schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
+  end
+
   desc 'Drops and recreates the database from db/schema.rb for the current environment and loads the seeds.'
   task :reset => [ 'db:drop', 'db:setup' ]