Made increment_counter/decrement_counter play nicely with optimistic locking, and added a more general update_counters method

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6139 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

4 files changed, 97 insertions, 4 deletions

diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index ba42776c7f..ed1b83cdca 100644
--- a/activerecord/CHANGELOG
+++ b/activerecord/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Made increment_counter/decrement_counter play nicely with optimistic locking, and added a more general update_counters method [Jamis Buck]
+
 * Reworked David's query cache to be available as Model.cache {...}. For the duration of the block no select query should be run more then once. Any inserts/deletes/executes will flush the whole cache however [Tobias Luetke]
   Task.cache { Task.find(1); Task.find(1) } #=> 1 query
   
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index af3d1997c5..2127f64a1b 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -519,18 +519,37 @@ module ActiveRecord #:nodoc:
         connection.select_value(sql, "#{name} Count").to_i
       end
 
+      # A generic "counter updater" implementation, intended primarily to be
+      # used by increment_counter and decrement_counter, but which may also
+      # be useful on its own. It simply does a direct SQL update for the record
+      # with the given ID, altering the given hash of counters by the amount
+      # given by the corresponding value:
+      #
+      #   Post.update_counters 5, :comment_count => -1, :action_count => 1
+      #   # UPDATE posts
+      #   #    SET comment_count = comment_count - 1,
+      #   #        action_count = action_count + 1
+      #   #  WHERE id = 5
+      def update_counters(id, counters)
+        updates = counters.inject([]) { |list, (counter_name, increment)|
+          sign = increment < 0 ? "-" : "+"
+          list << "#{counter_name} = #{counter_name} #{sign} #{increment.abs}"
+        }.join(", ")
+        update_all(updates, "#{primary_key} = #{quote_value(id)}")
+      end
+
       # Increments the specified counter by one. So <tt>DiscussionBoard.increment_counter("post_count",
       # discussion_board_id)</tt> would increment the "post_count" counter on the board responding to discussion_board_id.
       # This is used for caching aggregate values, so that they don't need to be computed every time. Especially important
       # for looping over a collection where each element require a number of aggregate values. Like the DiscussionBoard
       # that needs to list both the number of posts and comments.
       def increment_counter(counter_name, id)
-        update_all "#{counter_name} = #{counter_name} + 1", "#{primary_key} = #{quote_value(id)}"
+        update_counters(id, counter_name => 1)
       end
 
       # Works like increment_counter, but decrements instead.
       def decrement_counter(counter_name, id)
-        update_all "#{counter_name} = #{counter_name} - 1", "#{primary_key} = #{quote_value(id)}"
+        update_counters(id, counter_name => -1)
       end
 
 
diff --git a/activerecord/lib/active_record/locking/optimistic.rb b/activerecord/lib/active_record/locking/optimistic.rb
index 02cf565017..217bd3def7 100644
--- a/activerecord/lib/active_record/locking/optimistic.rb
+++ b/activerecord/lib/active_record/locking/optimistic.rb
@@ -31,14 +31,14 @@ module ActiveRecord
 
         base.alias_method_chain :update, :lock
         base.alias_method_chain :attributes_from_column_definition, :lock
-        
+
         class << base
           alias_method :locking_column=, :set_locking_column
         end
       end
 
       def locking_enabled? #:nodoc:
-        lock_optimistically && respond_to?(self.class.locking_column)
+        self.class.locking_enabled?
       end
 
       def attributes_from_column_definition_with_lock
@@ -80,6 +80,20 @@ module ActiveRecord
       module ClassMethods
         DEFAULT_LOCKING_COLUMN = 'lock_version'
 
+        def self.extended(base)
+          class <<base
+            alias_method_chain :update_counters, :lock
+          end
+        end
+
+        # Is optimistic locking enabled for this table? Returns true if the
+        # #lock_optimistically flag is set to true (which it is, by default)
+        # and the table includes the #locking_column column (defaults to
+        # lock_version).
+        def locking_enabled?
+          lock_optimistically && columns_hash[locking_column]
+        end
+
         # Set the column to use for optimistic locking. Defaults to lock_version.
         def set_locking_column(value = nil, &block)
           define_attr_method :locking_column, value, &block
@@ -100,6 +114,13 @@ module ActiveRecord
         def reset_locking_column
           set_locking_column DEFAULT_LOCKING_COLUMN
         end
+
+        # make sure the lock version column gets updated when counters are
+        # updated.
+        def update_counters_with_lock(id, counters)
+          counters = counters.merge(locking_column => 1) if locking_enabled?
+          update_counters_without_lock(id, counters)
+        end
       end
     end
   end
diff --git a/activerecord/test/locking_test.rb b/activerecord/test/locking_test.rb
index 471771bfbb..f62f1ac61c 100644
--- a/activerecord/test/locking_test.rb
+++ b/activerecord/test/locking_test.rb
@@ -1,5 +1,6 @@
 require 'abstract_unit'
 require 'fixtures/person'
+require 'fixtures/reader'
 require 'fixtures/legacy_thing'
 
 class LockWithoutDefault < ActiveRecord::Base; end
@@ -12,6 +13,11 @@ end
 class OptimisticLockingTest < Test::Unit::TestCase
   fixtures :people, :legacy_things
 
+  # need to disable transactional fixtures, because otherwise the sqlite3
+  # adapter (at least) chokes when we try and change the schema in the middle
+  # of a test (see test_increment_counter_*).
+  self.use_transactional_fixtures = false
+
   def test_lock_existing
     p1 = Person.find(1)
     p2 = Person.find(1)
@@ -73,6 +79,51 @@ class OptimisticLockingTest < Test::Unit::TestCase
     t1 = LockWithCustomColumnWithoutDefault.new
     assert_equal 0, t1.custom_lock_version
   end
+
+  { :lock_version => Person, :custom_lock_version => LegacyThing }.each do |name, model|
+    define_method("test_increment_counter_updates_#{name}") do
+      counter_test model, 1 do |id|
+        model.increment_counter :test_count, id
+      end
+    end
+
+    define_method("test_decrement_counter_updates_#{name}") do
+      counter_test model, -1 do |id|
+        model.decrement_counter :test_count, id
+      end
+    end
+
+    define_method("test_update_counters_updates_#{name}") do
+      counter_test model, 1 do |id|
+        model.update_counters id, :test_count => 1
+      end
+    end
+  end
+
+  private
+
+    def add_counter_column_to(model)
+      model.connection.add_column model.table_name, :test_count, :integer, :null => false, :default => 0
+      model.reset_column_information
+    end
+
+    def remove_counter_column_from(model)
+      model.connection.remove_column model.table_name, :test_count
+      model.reset_column_information
+    end
+
+    def counter_test(model, expected_count)
+      add_counter_column_to(model)
+      object = model.find(:first)
+      assert_equal 0, object.test_count
+      assert_equal 0, object.send(model.locking_column)
+      yield object.id
+      object.reload
+      assert_equal expected_count, object.test_count
+      assert_equal 1, object.send(model.locking_column)
+    ensure
+      remove_counter_column_from(model)
+    end
 end