lib/lhm/locked_switcher.rb in lhm-1.0.0.rc2 vs lib/lhm/locked_switcher.rb in lhm-1.0.0.rc3

@@ -1,31 +1,33 @@
-#
-#  Copyright (c) 2011, SoundCloud Ltd., Rany Keddo, Tobias Bielohlawek, Tobias
-#  Schmidt
-#
-#  Switches origin with destination table with a write lock. Use this as a safe
-#  alternative to rename, which can cause slave inconsistencies:
-#
-#    http://bugs.mysql.com/bug.php?id=39675
-#
-#  LockedSwitcher adopts the Facebook strategy, with the following caveat:
-#
-#    "Since alter table causes an implicit commit in innodb, innodb locks get
-#    released after the first alter table. So any transaction that sneaks in
-#    after the first alter table and before the second alter table gets
-#    a 'table not found' error. The second alter table is expected to be very
-#    fast though because copytable is not visible to other transactions and so
-#    there is no need to wait."
-#
+# Copyright (c) 2011, SoundCloud Ltd., Rany Keddo, Tobias Bielohlawek, Tobias
+# Schmidt
 
 require 'lhm/command'
 require 'lhm/migration'
+require 'lhm/sql_helper'
 
 module Lhm
+  # Switches origin with destination table with a write lock. Use this as
+  # a safe alternative to rename, which can cause slave inconsistencies:
+  #
+  #   http://bugs.mysql.com/bug.php?id=39675
+  #
+  # LockedSwitcher adopts the Facebook strategy, with the following caveat:
+  #
+  #   "Since alter table causes an implicit commit in innodb, innodb locks get
+  #   released after the first alter table. So any transaction that sneaks in
+  #   after the first alter table and before the second alter table gets
+  #   a 'table not found' error. The second alter table is expected to be very
+  #   fast though because copytable is not visible to other transactions and so
+  #   there is no need to wait."
+  #
   class LockedSwitcher
     include Command
+    include SqlHelper
 
+    attr_reader :connection
+
     def initialize(migration, connection = nil)
       @migration = migration
       @connection = connection
       @origin = migration.origin
       @destination = migration.destination
@@ -49,31 +51,25 @@
       [
         "set @lhm_auto_commit = @@session.autocommit",
         "set session autocommit = 0",
         yield,
         "set session autocommit = @lhm_auto_commit"
-
       ].flatten
     end
 
-    #
-    # Command interface
-    #
-
     def validate
       unless table?(@origin.name) && table?(@destination.name)
         error "`#{ @origin.name }` and `#{ @destination.name }` must exist"
       end
     end
 
+  private
+
     def revert
       sql "unlock tables"
     end
 
-  private
-
     def execute
       sql statements
     end
   end
 end
-