Ensure Model#destroy respects optimistic locking [#1966 state:resolved]

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

activerecord/lib/active_record/locking/optimistic.rb

@@ -23,6 +23,16 @@ module Locking
     #   p2.first_name = "should fail"
     #   p2.save # Raises a ActiveRecord::StaleObjectError
     #
+    # Optimistic locking will also check for stale data when objects are destroyed.  Example:
+    #
+    #   p1 = Person.find(1)
+    #   p2 = Person.find(1)
+    #
+    #   p1.first_name = "Michael"
+    #   p1.save
+    #
+    #   p2.destroy # Raises a ActiveRecord::StaleObjectError
+    #
     # You're then responsible for dealing with the conflict by rescuing the exception and either rolling back, merging,
     # or otherwise apply the business logic needed to resolve the conflict.
     #
@@ -39,6 +49,7 @@ def self.included(base) #:nodoc:
         base.lock_optimistically = true
 
         base.alias_method_chain :update, :lock
+        base.alias_method_chain :destroy, :lock
         base.alias_method_chain :attributes_from_column_definition, :lock
 
         class << base
@@ -98,6 +109,28 @@ def update_with_lock(attribute_names = @attributes.keys) #:nodoc:
           end
         end
 
+  def destroy_with_lock #:nodoc:
+    return destroy_without_lock unless locking_enabled?
+
+    unless new_record?
+      lock_col = self.class.locking_column
+      previous_value = send(lock_col).to_i
+
+      affected_rows = connection.delete(
+        "DELETE FROM #{self.class.quoted_table_name} " +
+        "WHERE #{connection.quote_column_name(self.class.primary_key)} = #{quoted_id} " +
+              "AND #{self.class.quoted_locking_column} = #{quote_value(previous_value)}",
+        "#{self.class.name} Destroy"
+      )
+
+      unless affected_rows == 1
+        raise ActiveRecord::StaleObjectError, "Attempted to delete a stale object"
+      end
+    end
+
+    freeze
+  end
+
       module ClassMethods
         DEFAULT_LOCKING_COLUMN = 'lock_version'
 

activerecord/test/cases/locking_test.rb

@@ -38,6 +38,24 @@ def test_lock_existing
     assert_raise(ActiveRecord::StaleObjectError) { p2.save! }
   end
 
+  def test_lock_destroy
+    p1 = Person.find(1)
+    p2 = Person.find(1)
+    assert_equal 0, p1.lock_version
+    assert_equal 0, p2.lock_version
+
+    p1.first_name = 'stu'
+    p1.save!
+    assert_equal 1, p1.lock_version
+    assert_equal 0, p2.lock_version
+
+    assert_raises(ActiveRecord::StaleObjectError) { p2.destroy }
+
+    assert p1.destroy
+    assert_equal true, p1.frozen?
+    assert_raises(ActiveRecord::RecordNotFound) { Person.find(1) }
+  end
+
   def test_lock_repeating
     p1 = Person.find(1)
     p2 = Person.find(1)