Fixing numeric attrs when set to same negative value

This bug occurs when an attribute of an ActiveRecord model is an
ActiveRecord::Type::Integer type or a ActiveRecord::Type::Decimal type (or any
other type that includes the ActiveRecord::Type::Numeric module. When the value
of the attribute is negative and is set to the same negative value, it is marked
as changed.

Take the following example of a Person model with the integer attribute age:

    class Person < ActiveRecord::Base
      # age          :integer(4)
    end

The following will produce the error:

    person = Person.new(age: -1)
    person.age = -1
    person.changes
    => { "age" => [-1, -1] }
    person.age_changed?
    => true

The problematic line is here:

    module ActiveRecord
      module Type
        module Numeric
          ...

          def non_numeric_string?(value)
            # 'wibble'.to_i will give zero, we want to make sure
            # that we aren't marking int zero to string zero as
            # changed.
            value.to_s !~ /\A\d+\.?\d*\z/
          end
        end
      end
    end

The regex match doesn't accept numbers with a leading '-'.

4 files changed, 18 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 6494c7374e..e5a4356523 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Fixes bug with 'ActiveRecord::Type::Numeric' that causes negative values to
+    be marked as having changed when set to the same negative value.
+
+    Closes GH#18161
+
+    *Daniel Fox*
+
 *   Introduce `force: :cascade` option for `create_table`. Using this option
     will recreate tables even if they have dependent objects (like foreign keys).
     `db/schema.rb` now uses `force: :cascade`. This makes it possible to
diff --git a/activerecord/lib/active_record/type/numeric.rb b/activerecord/lib/active_record/type/numeric.rb
index fa43266504..674f996f38 100644
--- a/activerecord/lib/active_record/type/numeric.rb
+++ b/activerecord/lib/active_record/type/numeric.rb
@@ -29,7 +29,7 @@ module ActiveRecord
         # 'wibble'.to_i will give zero, we want to make sure
         # that we aren't marking int zero to string zero as
         # changed.
-        value.to_s !~ /\A\d+\.?\d*\z/
+        value.to_s !~ /\A-?\d+\.?\d*\z/
       end
     end
   end
diff --git a/activerecord/test/cases/type/decimal_test.rb b/activerecord/test/cases/type/decimal_test.rb
index c028aa52af..34ed1d7b19 100644
--- a/activerecord/test/cases/type/decimal_test.rb
+++ b/activerecord/test/cases/type/decimal_test.rb
@@ -38,6 +38,14 @@ module ActiveRecord
         type = Decimal.new
         assert_equal BigDecimal("1"), type.type_cast_from_user(value)
       end
+
+      def test_changed?
+        type = Decimal.new
+
+        assert type.changed?(5.0, 5.0, '5.0wibble')
+        assert_not type.changed?(5.0, 5.0, '5.0')
+        assert_not type.changed?(-5.0, -5.0, '-5.0')
+      end
     end
   end
 end
diff --git a/activerecord/test/cases/type/integer_test.rb b/activerecord/test/cases/type/integer_test.rb
index 5942f77e18..af4d0b4642 100644
--- a/activerecord/test/cases/type/integer_test.rb
+++ b/activerecord/test/cases/type/integer_test.rb
@@ -47,6 +47,8 @@ module ActiveRecord
         assert type.changed?(5, 5, '5wibble')
         assert_not type.changed?(5, 5, '5')
         assert_not type.changed?(5, 5, '5.0')
+        assert_not type.changed?(-5, -5, '-5')
+        assert_not type.changed?(-5, -5, '-5.0')
         assert_not type.changed?(nil, nil, nil)
       end