Do not overwrite the database default value

When a new database record has a column that is set to its database
default value, the "#{attribute}_changed?" method returns false,
which causes default_value_for to overwrite the database default.

This commit changes this behavior to not overwrite when the column
is being set by the initialization attributes.

lib/default_value_for.rb

@@ -171,6 +171,20 @@ def set_default_values
                           end
         next unless connection_default_value_defined || attribute_blank
 
+        attribute_init_value_defined = @initialization_attributes.is_a?(Hash) &&
+          (
+            (
+              @initialization_attributes.has_key?(attribute) &&
+              @initialization_attributes[attribute].present?
+            ) ||
+            (
+              @initialization_attributes.has_key?("#{attribute}_attributes") &&
+              nested_attributes_options.stringify_keys[attribute].present?
+            )
+          )
+
+        next if attribute_init_value_defined
+
         # allow explicitly setting nil through allow nil option
         next if @initialization_attributes.is_a?(Hash) &&
                 (

test.rb

@@ -168,6 +168,11 @@ def test_overwrites_db_default
     assert_equal 1234, Book.new.count
   end
 
+  def test_does_not_overwrite_db_default_if_provided_by_mass_assignment
+    Book.default_value_for(:count, :allows_nil => false) { 1234 }
+    assert_equal Book.column_defaults['count'], Book.new(count: Book.column_defaults['count']).count
+  end
+
   def test_doesnt_overwrite_values_provided_by_mass_assignment
     Book.default_value_for :number, 1234
     assert_equal 1, Book.new(:number => 1, :count => 2).number
@@ -199,6 +204,11 @@ def test_overwrites_explicitly_provided_nil_values_in_mass_assignment
     assert_equal 1234, Book.new(:number => nil).number
   end
 
+  def test_overwrites_string_blank_value_in_mass_assignment
+    Book.default_value_for(:type, :allows_nil => false) { 'string' }
+    assert_equal 'string', Book.new(type: '').type
+  end
+
   def test_default_values_are_inherited
     Book.default_value_for :number, 1234
     assert_equal 1234, Novel.new.number