想让unique验证实现ajax验证,除了修改rules需要改2个地方
1.view里面
$form->field($model, 'ID',['enableAjaxValidation'=>true]);

2.controller里面

use yii\web\Response;
use yii\widgets\ActiveForm;
if (Yii::$app->request->isAjax && $model->load(Yii::$app->request->post())) {
    Yii::$app->response->format = Response::FORMAT_JSON;           
    return ActiveForm::validate($model);  	      
}elseif($model->load(Yii::$app->request->post())){
    $model->save();
    ....
}