diff --git a/common/Alias/Model.php b/common/Alias/Model.php
index 4fed3ec..490aafc 100644
--- a/common/Alias/Model.php
+++ b/common/Alias/Model.php
@@ -124,13 +124,13 @@ abstract class Model extends BaseModel implements ModelInterface {
   }
 
   protected static function parseInput($input): array {
-    return array_intersect_key((array) $input, array_combine(self::$fields, self::$fields));
+    return array_intersect_key((array) $input, array_combine(static::$fields, static::$fields));
   }
-  public static function add(ModelFactory $factory, $input): bool {
-    $data = self::parseInput($input);
+  public static function add(ModelFactory $factory, $input): ?ModelInterface {
+    $data = static::parseInput($input);
     $class = get_called_class();
     if (method_exists($class, 'find')) {
-      $obj = self::find($factory, $input);
+      $obj = static::find($factory, $input);
     } else {
       $where = $data;
       $where = array_values(array_walk($where, function(&$item, $key) {
@@ -138,22 +138,18 @@ abstract class Model extends BaseModel implements ModelInterface {
       }));
       $obj = $factory->find($class)->where($where)->one();
     }
-    if ($obj === false) {
+    if ($obj === null) {
       $obj = $factory->create($class, $data);
-      return $obj->save();
     }
-    return false;
+    return $obj;
   }
   public function edit($input): bool {
-    $data = self::parseInput($input);
-    foreach (self::$fields as $field) {
+    $data = static::parseInput($input);
+    foreach (static::$fields as $field) {
       if ($this->{$field} != $data[$field]) {
         $this->{$field} = $data[$field];
       }
     }
-    if ($this->isDirty()) {
-      return $this->save();
-    }
-    return false;
+    return $this->save();
   }
 }
diff --git a/common/Define/Model.php b/common/Define/Model.php
index bce472d..5e220c6 100644
--- a/common/Define/Model.php
+++ b/common/Define/Model.php
@@ -12,6 +12,6 @@ interface Model {
 
   public function toArray(): array;
 
-  public static function add(ModelFactory $factory, $input): bool;
+  public static function add(ModelFactory $factory, $input): ?Model;
   public function edit($input): bool;
 }