Do not create table_name_prefix method on isolated module if the method already exists.

Signed-off-by: José Valim <jose.valim@gmail.com>

2 files changed, 23 insertions, 2 deletions

diff --git a/railties/lib/rails/engine.rb b/railties/lib/rails/engine.rb
index 62fb781c19..85fa4424c4 100644
--- a/railties/lib/rails/engine.rb
+++ b/railties/lib/rails/engine.rb
@@ -363,8 +363,10 @@ module Rails
               _railtie
             end
 
-            define_method(:table_name_prefix) do
-              "#{name}_"
+            unless mod.respond_to?(:table_name_prefix)
+              define_method(:table_name_prefix) do
+                "#{name}_"
+              end
             end
          end
         end
diff --git a/railties/test/railties/engine_test.rb b/railties/test/railties/engine_test.rb
index 701b6816c8..7548c6318e 100644
--- a/railties/test/railties/engine_test.rb
+++ b/railties/test/railties/engine_test.rb
@@ -683,5 +683,24 @@ module RailtiesTest
       app_generators = Rails.application.config.generators.options[:rails]
       assert_equal :test_unit    , app_generators[:test_framework]
     end
+
+    test "do not create table_name_prefix method if it already exists" do
+      @plugin.write "lib/bukkits.rb", <<-RUBY
+        module Bukkits
+          def self.table_name_prefix
+            "foo"
+          end
+
+          class Engine < ::Rails::Engine
+            isolate_namespace(Bukkits)
+          end
+        end
+      RUBY
+
+      boot_rails
+      require "#{rails_root}/config/environment"
+
+      assert_equal "foo", Bukkits.table_name_prefix
+    end
   end
 end