Optimistic locking: gracefully handle nil versions, treat as zero. Closes #5908.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4958 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

4 files changed, 43 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index 460d7f5f3f..719ae56748 100644
--- a/activerecord/CHANGELOG
+++ b/activerecord/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Optimistic locking: gracefully handle nil versions, treat as zero.  #5908 [Tom Ward]
+
 * validates_confirmation_of only kicks in when the attribute, rather than its confirmation, is present.  #785 [z@wzph.com]
 
 * to_xml: the :methods option works on arrays of records.  #5845 [Josh Starcher]
diff --git a/activerecord/lib/active_record/locking/optimistic.rb b/activerecord/lib/active_record/locking/optimistic.rb
index 7bae573924..823f4e19fc 100644
--- a/activerecord/lib/active_record/locking/optimistic.rb
+++ b/activerecord/lib/active_record/locking/optimistic.rb
@@ -30,6 +30,8 @@ module ActiveRecord
         base.lock_optimistically = true
 
         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
@@ -39,6 +41,21 @@ module ActiveRecord
         lock_optimistically && respond_to?(self.class.locking_column)
       end
 
+      def attributes_from_column_definition_with_lock
+        result = attributes_from_column_definition_without_lock
+        
+        # If the locking column has no default value set,
+        # start the lock version at zero.  Note we can't use
+        # locking_enabled? at this point as @attributes may
+        # not have been initialized yet
+        
+        if lock_optimistically && result.include?(self.class.locking_column)
+          result[self.class.locking_column] ||= 0
+        end
+        
+        return result
+      end
+
       def update_with_lock #:nodoc:
         return update_without_lock unless locking_enabled?
 
diff --git a/activerecord/test/fixtures/db_definitions/schema.rb b/activerecord/test/fixtures/db_definitions/schema.rb
index e06c14b6ae..6f4aca971e 100644
--- a/activerecord/test/fixtures/db_definitions/schema.rb
+++ b/activerecord/test/fixtures/db_definitions/schema.rb
@@ -49,4 +49,12 @@ ActiveRecord::Schema.define do
     t.column :sink_id,   :integer, :null => false
   end
   add_index :edges, [:source_id, :sink_id], :unique => true, :name => 'unique_edge_index'
+
+  create_table :lock_without_defaults, :force => true do |t|
+    t.column :lock_version, :integer
+  end
+  
+  create_table :lock_with_custom_column_without_defaults, :force => true do |t|
+    t.column :custom_lock_version, :integer
+  end
 end
diff --git a/activerecord/test/locking_test.rb b/activerecord/test/locking_test.rb
index 00df4bb8e4..80f0dc8496 100644
--- a/activerecord/test/locking_test.rb
+++ b/activerecord/test/locking_test.rb
@@ -2,6 +2,12 @@ require 'abstract_unit'
 require 'fixtures/person'
 require 'fixtures/legacy_thing'
 
+class LockWithoutDefault < ActiveRecord::Base; end
+
+class LockWithCustomColumnWithoutDefault < ActiveRecord::Base
+  set_locking_column :custom_lock_version
+end
+
 class OptimisticLockingTest < Test::Unit::TestCase
   fixtures :people, :legacy_things
 
@@ -56,6 +62,16 @@ class OptimisticLockingTest < Test::Unit::TestCase
     assert_equal 1, p1.lock_version
     assert_equal p1.lock_version, Person.new(p1.attributes).lock_version
   end
+  
+  def test_lock_without_default_sets_version_to_zero
+    t1 = LockWithoutDefault.new
+    assert_equal 0, t1.lock_version
+  end
+  
+  def test_lock_with_custom_column_without_default_sets_version_to_zero
+    t1 = LockWithCustomColumnWithoutDefault.new
+    assert_equal 0, t1.custom_lock_version
+  end
 end