Raise error when trying to change model based currency

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ## master (next release)
+- Raise error when trying to change model based currency
 - Add testing tasks for rails 4.x
 - Fix issue with Numeric values in MoneyValidator (GH-83).
 - Fix test helper

CONTRIBUTORS

@@ -11,6 +11,7 @@ Carlos Hernandez
 Carlos Hernández
 Clarke Brunsdon
 Dan Beaulieu
+Danil Pismenny
 Deepak Kannan
 Derek Bender
 Dmitriy Dudkin

lib/money-rails/active_record/monetizable.rb

@@ -150,6 +150,17 @@ def monetized_attributes
             # Update cents
             send("#{subunit_name}=", money.try(:cents))
 
+            money_currency = money.try(:currency)
+
+            if self.respond_to?("#{instance_currency_name}=")
+              send("#{instance_currency_name}=", money_currency.try(:iso_code))
+            else
+              current_currency = send("currency_for_#{name}")
+              if money_currency && current_currency != money_currency
+                raise "Can't change readonly currency '#{current_currency}' to '#{money_currency}' for field '#{name}'"
+              end
+            end
+
             # Update currency iso value if there is an instance currency attribute
             if instance_currency_name.present? &&
               self.respond_to?("#{instance_currency_name}=")

spec/active_record/monetizable_spec.rb

@@ -47,6 +47,13 @@ class Sub < Product; end
         product.price_cents.should == 215
       end
 
+      it "should raise error if can't change currency" do
+        product = Product.new
+        expect {
+          product.price Money.new(10,'RUB')
+        }.to raise_error
+      end
+
       it "respects :as argument" do
         product.discount_value.should == Money.new(150, "USD")
       end
@@ -389,11 +396,30 @@ class Sub < Product; end
           product = Product.create(:sale_price_amount => 1234)
           product.sale_price.currency_as_string == 'USD'
         end
+
         it "is overridden by instance currency column" do
           product = Product.create(:sale_price_amount => 1234,
                                    :sale_price_currency_code => 'CAD')
           product.sale_price.currency_as_string.should == 'CAD'
         end
+
+        it 'can change currency of custom column' do
+          product = Product.create!(
+            :price => Money.new(10,'USD'),
+            :bonus => Money.new(10,'GBP'),
+            :discount => 10,
+            :sale_price_amount => 1234,
+            :sale_price_currency_code => 'USD')
+
+          product.sale_price.currency_as_string.should == 'USD'
+
+          product.sale_price = Money.new 456, 'CAD'
+          product.save
+          product.reload
+
+          product.sale_price.currency_as_string.should == 'CAD'
+          product.discount_value.currency_as_string.should == 'USD'
+        end
       end
 
       context "for model with currency column:" do