Clear prefix_parameters cache when setting prefix

activeresource/lib/active_resource/base.rb

@@ -356,6 +356,9 @@ def prefix=(value = '/')
         # Replace :placeholders with '#{embedded options[:lookups]}'
         prefix_call = value.gsub(/:\w+/) { |key| "\#{options[#{key}]}" }
 
+        # Clear prefix parameters in case they have been cached
+        @prefix_parameters = nil
+
         # Redefine the new methods.
         code = <<-end_code
           def prefix_source() "#{value}" end

activeresource/test/base_test.rb

@@ -485,6 +485,15 @@ def test_set_prefix_with_inline_keys
     end
   end
 
+  def test_set_prefix_twice_should_clear_params
+    SetterTrap.rollback_sets(Person) do |person_class|
+      person_class.prefix = "the_prefix/:the_param1"
+      assert_equal Set.new([:the_param1]), person_class.prefix_parameters
+      person_class.prefix = "the_prefix/:the_param2"
+      assert_equal Set.new([:the_param2]), person_class.prefix_parameters
+    end
+  end
+
   def test_set_prefix_with_default_value
     SetterTrap.rollback_sets(Person) do |person_class|
       person_class.set_prefix