Destroy respects optimistic locking.

Now works with :dependent => :destroy and includes unit tests for that
case.  Also includes better error messages when updating/deleting stale
objects.

[#1966 state:committed]

Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>

activerecord/CHANGELOG

@@ -1,5 +1,7 @@
 *2.3.6 (pending)*
 
+* Destroy uses optimistic locking. If lock_version on the record you're destroying doesn't match lock_version in the database, a StaleObjectError is raised.  #1966 [Curtis Hawthorne]
+
 * To prefix the table names of all models in a module, define self.table_name_prefix on the module.  #4032 [Andrew White]
 
 * Association inverses for belongs_to, has_one, and has_many. Optimization to reduce database queries.  #3533 [Murray Steele]

activerecord/lib/active_record/associations.rb

@@ -1419,7 +1419,16 @@ def configure_dependency_for_has_many(reflection, extra_conditions = nil)
               when :destroy
                 method_name = "has_many_dependent_destroy_for_#{reflection.name}".to_sym
                 define_method(method_name) do
-                  send(reflection.name).each { |o| o.destroy }
+                  send(reflection.name).each do |o|
+                    # No point in executing the counter update since we're going to destroy the parent anyway
+                    counter_method = ('belongs_to_counter_cache_before_destroy_for_' + self.class.name.downcase).to_sym
+                    if(o.respond_to? counter_method) then
+                      class << o
+                        self
+                      end.send(:define_method, counter_method, Proc.new {})
+                    end
+                    o.destroy
+                  end
                 end
                 before_destroy method_name
               when :delete_all

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
@@ -86,7 +97,7 @@ def update_with_lock(attribute_names = @attributes.keys) #:nodoc:
             end_sql
 
             unless affected_rows == 1
-              raise ActiveRecord::StaleObjectError, "Attempted to update a stale object"
+              raise ActiveRecord::StaleObjectError, "Attempted to update a stale object: #{self.class.name}"
             end
 
             affected_rows
@@ -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: #{self.class.name}"
+            end
+          end
+
+          freeze
+        end
+
       module ClassMethods
         DEFAULT_LOCKING_COLUMN = 'lock_version'
 

activerecord/test/cases/locking_test.rb

@@ -38,6 +38,25 @@ def test_lock_existing
     assert_raise(ActiveRecord::StaleObjectError) { p2.save! }
   end
 
+  # See Lighthouse ticket #1966
+  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)
@@ -150,6 +169,32 @@ def test_readonly_attributes
       end
     end
   end
+
+  # See Lighthouse ticket #1966
+  def test_destroy_dependents
+    # Establish dependent relationship between People and LegacyThing
+    add_counter_column_to(Person, 'legacy_things_count')
+    LegacyThing.connection.add_column LegacyThing.table_name, 'person_id', :integer
+    LegacyThing.reset_column_information
+    LegacyThing.class_eval do
+      belongs_to :person, :counter_cache => true
+    end
+    Person.class_eval do
+      has_many :legacy_things, :dependent => :destroy
+    end
+
+    # Make sure that counter incrementing doesn't cause problems
+    p1 = Person.new(:first_name => 'fjord')
+    p1.save!
+    t = LegacyThing.new(:person => p1)
+    t.save!
+    p1.reload
+    assert_equal 1, p1.legacy_things_count
+    assert p1.destroy
+    assert_equal true, p1.frozen?
+    assert_raises(ActiveRecord::RecordNotFound) { Person.find(p1.id) }
+    assert_raises(ActiveRecord::RecordNotFound) { LegacyThing.find(t.id) }
+  end
 
   def test_quote_table_name
     ref = references(:michael_magician)
@@ -168,11 +213,11 @@ def test_update_without_attributes_does_not_only_update_lock_version
 
   private
 
-    def add_counter_column_to(model)
-      model.connection.add_column model.table_name, :test_count, :integer, :null => false, :default => 0
+    def add_counter_column_to(model, col='test_count')
+      model.connection.add_column model.table_name, col, :integer, :null => false, :default => 0
       model.reset_column_information
       # OpenBase does not set a value to existing rows when adding a not null default column
-      model.update_all(:test_count => 0) if current_adapter?(:OpenBaseAdapter)
+      model.update_all(col => 0) if current_adapter?(:OpenBaseAdapter)
     end
 
     def remove_counter_column_from(model)