不要updated字段，created_at用时间戳
`[

			'class' => TimestampBehavior::className(),
			'updatedAtAttribute' => false,
			'value' => time(),
		], `

UploadedFile::getInstanceByName('file');
By Name !!!
我也被困扰了好久，最终解决了，如果使用了$model->save(); 还要记得
$this->file->saveAs($this->getFilePath($this->getFileName()), false); 这句里面的false，不然报错，找不到此文件。

以下是完整代码

model:

['file', 'file', 'skipOnEmpty' => true, 'mimeTypes' => 'image/*, video/*, audio/*, application/zip, application/pdf', 'wrongMimeType' =>'禁止的文件类型',  'tooBig' => '文件太大，仅允许{formattedLimit}']
        ];
public function upload(){
		$this->file  = UploadedFile::getInstanceByName('file');
		if($this->validate()){
			$this->file->saveAs($this->getFilePath($this->getFileName()), false);
			return true;
		}
		return false;
	}
    
    controller：
     public function actionCreate() {
		
		$model = new Media();
		if ( isset( $_FILES["file"] ) && !empty( $_FILES["file"]["name"] ) ) {
			Yii::$app->response->format = 'json';
			if($model->upload()){
					$model->src = $model->getSrc();
					if($model->save()){
						return ['url' => $model->getUrl($model->getFileName())];
					}
			} 
			return $model->errors; 
		}  
		return $this->renderPartial('create', ['model' => $model]);    
    }
    
    JQ: 
     $('html, .upload-area').on('dragenter dragover drop', function (e) { 
	e.stopPropagation();  
	e.preventDefault(); 
	$('.upload-message').text('拖放到这里');
});

 $('.modal').on('click','.upload-area',function(){
	$('#file').click();
});

$('.modal').on('drop', '.upload-area',function (e) {
    e.stopPropagation();
    e.preventDefault();
    var files = e.originalEvent.dataTransfer.files;
    var formData = new FormData();

	$.each(files, function(i, file) {
		formData.append('file', files[i]);
		uploadData(formData);
	});  
});

$('.modal').on('change','#file',function(){
	var formData = new FormData();
	$.each($('#file')[0].files, function(i, file) {
		formData.append('file', $('#file')[0].files[i]);
		uploadData(formData);
	});
});

function uploadData(formData){
    $.ajax({
        url: '/media/create',
        type: 'post',
        data: formData,
        contentType: false,
        processData: false,
        dataType: 'json',
		beforeSend:function(){ $('.upload-message').text("上传中...");},
        success: function(response){
			if(response.url){
				$('.upload-message').html(response.url);
				$.pjax.reload({container: '#pjax'});
			}else{
				$('.upload-message').html(response.file);
			} 
        }
    });
}


HTML:
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
<b class="upload-title">上传文件</b>
</div>
<div class="modal-body upload-file">
<input type="file" name="file" id="file" multiple>
<div class="upload-area">
<div class="upload-message">拖文件到这儿<br/>或<br/>点击选择 </div>	
</div>
</div>