Change field_changed? method to handle the case where a nullable integer...

Change field_changed? method to handle the case where a nullable integer column is changed from 0 to '0'

[#1530 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

activerecord/lib/active_record/dirty.rb

@@ -151,12 +151,12 @@ def update_with_dirty
 
       def field_changed?(attr, old, value)
         if column = column_for_attribute(attr)
-          if column.type == :integer && column.null && (old.nil? || old == 0)
+          if column.type == :integer && column.null && (old.nil? || old == 0) && value.blank?
             # For nullable integer columns, NULL gets stored in database for blank (i.e. '') values.
             # Hence we don't record it as a change if the value changes from nil to ''.
             # If an old value of 0 is set to '' we want this to get changed to nil as otherwise it'll
             # be typecast back to 0 (''.to_i => 0)
-            value = nil if value.blank?
+            value = nil
           else
             value = column.type_cast(value)
           end

activerecord/test/cases/dirty_test.rb

@@ -68,6 +68,18 @@ def test_nullable_integer_not_marked_as_changed_if_new_value_is_blank
     end
   end
 
+  def test_nullable_integer_zero_to_string_zero_not_marked_as_changed
+    pirate = Pirate.new
+    pirate.parrot_id = 0
+    pirate.catchphrase = 'arrr'
+    assert pirate.save!
+
+    assert !pirate.changed?
+
+    pirate.parrot_id = '0'
+    assert !pirate.changed?
+  end
+
   def test_zero_to_blank_marked_as_changed
     pirate = Pirate.new
     pirate.catchphrase = "Yarrrr, me hearties"