MySQL: rename_column preserves default values. [#466 state:resolved]

activerecord/CHANGELOG

@@ -1,5 +1,7 @@
 *Edge*
 
+* MySQL: rename_column preserves column defaults.  #466 [Diego Algorta]
+
 * Add :from option to calculations.  #397 [Ben Munat]
 
 * Add :validate option to associations to enable/disable the automatic validation of associated models. Resolves #301. [Jan De Poorter]

activerecord/lib/active_record/connection_adapters/mysql_adapter.rb

@@ -450,8 +450,16 @@ module ActiveRecord
       end
 
       def rename_column(table_name, column_name, new_column_name) #:nodoc:
+        options = {}
+        if column = columns(table_name).find { |c| c.name == column_name.to_s }
+          options[:default] = column.default
+        else
+          raise ActiveRecordError, "No such column: #{table_name}.#{column_name}"
+        end
         current_type = select_one("SHOW COLUMNS FROM #{quote_table_name(table_name)} LIKE '#{column_name}'")["Type"]
-        execute "ALTER TABLE #{quote_table_name(table_name)} CHANGE #{quote_column_name(column_name)} #{quote_column_name(new_column_name)} #{current_type}"
+        rename_column_sql = "ALTER TABLE #{quote_table_name(table_name)} CHANGE #{quote_column_name(column_name)} #{quote_column_name(new_column_name)} #{current_type}"
+        add_column_options!(rename_column_sql, options)
+        execute(rename_column_sql)
       end
 
       # Maps logical Rails types to MySQL-specific data types.

activerecord/test/cases/migration_test.rb

@@ -483,6 +483,32 @@ if ActiveRecord::Base.connection.supports_migrations?
       end
     end
 
+    def test_rename_column_preserves_default_value_not_null
+      begin
+        default_before = Developer.connection.columns("developers").find { |c| c.name == "salary" }.default
+        assert_equal 70000, default_before
+        Developer.connection.rename_column "developers", "salary", "anual_salary"
+        Developer.reset_column_information
+        assert Developer.column_names.include?("anual_salary")
+        default_after = Developer.connection.columns("developers").find { |c| c.name == "anual_salary" }.default
+        assert_equal 70000, default_after
+      ensure
+        Developer.connection.rename_column "developers", "anual_salary", "salary"
+        Developer.reset_column_information
+      end
+    end
+
+    def test_rename_nonexistent_column
+      ActiveRecord::Base.connection.create_table(:hats) do |table|
+        table.column :hat_name, :string, :default => nil
+      end
+      assert_raises(ActiveRecord::ActiveRecordError) do
+        Person.connection.rename_column "hats", "nonexistent", "should_fail"
+      end
+    ensure
+      ActiveRecord::Base.connection.drop_table(:hats)
+    end
+
     def test_rename_column_with_sql_reserved_word
       begin
         assert_nothing_raised { Person.connection.rename_column "people", "first_name", "group" }