[
'attribute' => 'created_at',
'value' => function ($model) {
return date('Y-m-d H:i:s', $model->created_at);
},
],
[
'attribute' => 'created_at',
'format' => ['date', 'Y-m-d H:i:s'],
],

$query->andFilterWhere([
// ......
'created_at' => $this->created_at,
// ......
]);

//我们搜索输入框中输入的格式一般是 2016-01-01 而非时间戳
//输出2016-01-01无非是想搜索这一天的数据，因此代码如下
if ($this->created_at) {
$createdAt = strtotime($this->created_at);
$createdAtEnd = $createdAt + 24*3600;
$query->andWhere("created_at >= {$createdAt} AND created_at <= {$createdAtEnd}");
}