diff --git a/library/think/db/Builder.php b/library/think/db/Builder.php
index b141a8b7..1fa2968a 100644
--- a/library/think/db/Builder.php
+++ b/library/think/db/Builder.php
@@ -98,15 +98,16 @@ abstract class Builder
         $result = [];
         foreach ($data as $key => $val) {
             $item = $this->parseKey($key, $options);
+            if (is_object($val) && method_exists($val, '__toString')) {
+                // 对象数据写入
+                $val = $val->__toString();
+            }
             if (false === strpos($key, '.') && !in_array($key, $fields, true)) {
                 if ($options['strict']) {
                     throw new Exception('fields not exists:[' . $key . ']');
                 }
             } elseif (is_null($val)) {
                 $result[$item] = 'NULL';
-            } elseif (is_object($val) && method_exists($val, '__toString')) {
-                // 对象数据写入
-                $result[$item] = $val->__toString();
             } elseif (isset($val[0]) && 'exp' == $val[0]) {
                 $result[$item] = $val[1];
             } elseif (is_scalar($val)) {