diff --git a/doitphp/core/Model.class.php b/doitphp/core/Model.class.php
index b2c461c..eb076f5 100644
--- a/doitphp/core/Model.class.php
+++ b/doitphp/core/Model.class.php
@@ -492,7 +492,7 @@ public function lastInsertId() {
      */
     public function startTrans() {
 
-        return $this->_master->startTrans();
+        return $this->_master()->startTrans();
     }
 
     /**
@@ -503,7 +503,7 @@ public function startTrans() {
      */
     public function commit() {
 
-        return $this->_master->commit();
+        return $this->_master()->commit();
     }
 
     /**
@@ -514,7 +514,7 @@ public function commit() {
      */
     public function rollback() {
 
-        return $this->_master->rollback();
+        return $this->_master()->rollback();
     }
 
     /**
@@ -1674,4 +1674,4 @@ public static function getInstance() {
 
         return self::$_instance;
     }
-}
\ No newline at end of file
+}