Ignore converted methods when writing cents

Gemfile

@@ -9,7 +9,7 @@ platforms :jruby do
 end
 
 platforms :ruby do
-  gem "sqlite3"
+  gem "sqlite3", "~> 1.4"
 end
 
 platform :mri do

lib/money-rails/active_record/monetizable.rb

@@ -132,7 +132,7 @@ def monetize(*fields)
               # the subunit value directly
               define_method "#{subunit_name}=" do |value|
                 instance_variable_set "@#{name}_money_before_type_cast", nil
-                write_attribute(subunit_name, value)
+                write_cents(subunit_name, value)
               end
             end
 
@@ -205,7 +205,7 @@ def read_monetized(name, subunit_name, options = nil, *args, **kwargs)
             result = memoized
           else
             memoized_amount = memoized.amount.to_money(attr_currency)
-            write_attribute subunit_name, memoized_amount.cents
+            write_cents subunit_name, memoized_amount.cents
             # Cache the value (it may be nil)
             result = instance_variable_set("@#{name}", memoized_amount)
           end
@@ -262,9 +262,9 @@ def write_monetized(name, subunit_name, value, validation_enabled, instance_curr
           # (Note: 'attribute_aliases' doesn't exist in Rails 3.x, so we
           # can't tell if the attribute was aliased.)
           original_name = self.class.attribute_aliases[subunit_name.to_s]
-          write_attribute(original_name, money.try(:cents))
+          write_cents(original_name, money.try(:cents))
         else
-          write_attribute(subunit_name, money.try(:cents))
+          write_cents(subunit_name, money.try(:cents))
         end
 
         if money_currency = money.try(:currency)
@@ -299,6 +299,13 @@ def currency_for(name, instance_currency_name, field_currency_name)
           Money.default_currency
         end
       end
+
+      def write_cents(attribute_name, cents)
+        # ignore converted methods
+        return unless has_attribute? attribute_name
+
+        write_attribute(attribute_name, cents)
+      end
     end
   end
 end

spec/active_record/monetizable_spec.rb

@@ -105,6 +105,14 @@ def assert_monetized_attributes(monetized_attributes, expected_attributes)
         expect(transaction.amount_cents).to eq(20000)
       end
 
+      it "update to instance currency field gets applied to converted methods" do
+        transaction = Transaction.create(amount: '200', tax: '10', currency: 'USD')
+        expect(transaction.total).to eq(Money.new(21000, 'USD'))
+
+        transaction.currency = 'CAD'
+        expect(transaction.total).to eq(Money.new(21000, 'CAD'))
+      end
+
       it "raises an error if trying to create two attributes with the same name" do
         expect do
           class Product