diff --git a/dblayer.php b/dblayer.php
index db9765a..d830d1f 100644
--- a/dblayer.php
+++ b/dblayer.php
@@ -173,7 +173,8 @@ class dblayer extends PDO
     return $res;
   }
 
-  /** Update the key tuple with the provided datas */
+  /** Update the key tuple with the provided datas 
+      Return the number of rows modified */
   function update ($updatekey, $datas)
   {
     if ($this->db === null)
@@ -186,6 +187,8 @@ class dblayer extends PDO
       if (array_key_exists ($key, $datas))
         $datasOK[$key] = $datas[$key];
     }
+    if (count ($datasOK) === 0)
+      throw new Exception (_("Don't receive any field to display"), 501);
 
     $req = "UPDATE `".$this->table."` SET ";
     $i = 0;
@@ -218,6 +221,7 @@ class dblayer extends PDO
     }
 
     $st->execute ();
+    return $st->rowCount();
   }
 
   /** Delete a tuple identified by its primary key