Add transaction as MSSQL alter table is transactional

Author: lafriks

models/migrations/migrations.go

@@ -239,6 +239,11 @@ func dropTableColumns(x *xorm.Engine, tableName string, columnNames ...string) (
 	case setting.UseMSSQL:
 		sess := x.NewSession()
 		defer sess.Close()
+
+		if err = sess.Begin(); err != nil {
+			return err
+		}
+
 		cols := ""
 		for _, col := range columnNames {
 			if cols != "" {
@@ -250,16 +255,21 @@ func dropTableColumns(x *xorm.Engine, tableName string, columnNames ...string) (
 			tableName, strings.Replace(cols, "`", "'", -1))
 		constraints := make([]string, 0)
 		if err := sess.SQL(sql).Find(&constraints); err != nil {
+			sess.Rollback()
 			return fmt.Errorf("Find constraints: %v", err)
 		}
 		for _, constraint := range constraints {
 			if _, err := sess.Exec(fmt.Sprintf("ALTER TABLE `%s` DROP CONSTRAINT `%s`", tableName, constraint)); err != nil {
+				sess.Rollback()
 				return fmt.Errorf("Drop table `%s` constraint `%s`: %v", tableName, constraint, err)
 			}
 		}
 		if _, err := sess.Exec(fmt.Sprintf("ALTER TABLE `%s` DROP COLUMN %s", tableName, cols)); err != nil {
+			sess.Rollback()
 			return fmt.Errorf("Drop table `%s` columns %v: %v", tableName, columnNames, err)
 		}
+
+		return sess.Commit()
 	default:
 		log.Fatal(4, "Unrecognized DB")
 	}