diff --git a/library/think/Model.php b/library/think/Model.php
index 9903370b..2179920d 100644
--- a/library/think/Model.php
+++ b/library/think/Model.php
@@ -859,10 +859,10 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
 
     /**
      * 初始化数据库对象
-     * @access public
+     * @access protected
      * @return \think\db\Query
      */
-    public static function db()
+    protected static function db()
     {
         $model = get_called_class();
         if (!isset(self::$links[$model])) {
@@ -894,7 +894,7 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
             call_user_func_array([$this, $method], $args);
             return $this;
         } else {
-            throw new Exception(__CLASS__ . ':' . $method . ' method not exist');
+            return call_user_func_array([self::db(), $method], $args);
         }
     }
 
diff --git a/library/think/model/Merge.php b/library/think/model/Merge.php
index 6f35b297..05918fac 100644
--- a/library/think/model/Merge.php
+++ b/library/think/model/Merge.php
@@ -66,7 +66,7 @@ class Merge extends Model
 
         foreach (static::$relationModel as $key => $model) {
             $name  = is_int($key) ? $model : $key;
-            $table = is_int($key) ? self::db()->getTable($name) : $model;
+            $table = is_int($key) ? $query->getTable($name) : $model;
             $query->join($table . ' ' . $name, $name . '.' . $class->fk . '=' . $master . '.' . $class->getPk());
             $fields = self::getModelField($name, $table, $class->mapFields);
             $query->field($fields);