购物车数量错误

@@ -57,7 +57,7 @@ class Cart extends Api
         $spec_info = $spec_sku->where('goods_spec_id', $sku_id)->find();
         if ($cart) {
 
-            if ($spec_info['stock_num'] + $cart['number'] < $number) {
+            if ( $number+ $cart['number'] < $spec_info['stock_num']) {
                 $this->error('库存不足');
             }
             $cart->setInc('number', $number);