Yii验证表格表单不能上传文件

当我尝试在我的模型的多个实例(表格方式)中上传多个文件时，我遇到了一些问题。

我有一个名为Files的模型和一个为该模型的多个实例生成表单的视图。当我保存没有"multipart/form-data"的表单时，一切正常，但是如果我将这个参数放在表单上并提交它，验证将显示"File不能为空"的消息。

请看下面我的控制器代码:

public function actionRegistration() {
  $company  = new Company;
  $contacts = $this->getModelItens('Contact', 3);
  $banks    = $this->getModelItens('Bank'   , 2);
  $files    = $this->getModelItens('File'   , 2);
  $company->scenario = 'create';
  if($_POST['Company']) {
    $company->attributes = $_POST['Company'];
    $valid = $company->validate();
    $valid = $this->validateModels($_POST['Contact'], $contacts) && $valid;
    $valid = $this->validateModels($_POST['Bank'], $banks) && $valid;
    $valid = $this->validateModels($_POST['File'], $files) && $valid;
    if($valid) {
      if($company->save()) {
        $this->saveModels($contacts, $company->id);
        $this->saveModels($banks, $company->id);
        $this->saveModels($files, $company->id);
        $this->redirect('/obrigado');
      }
    }
  }
    $this->render('registration', array('company' => $company, 'contacts' => $contacts, 'banks' => $banks, 'files' => $files));
  }

private function getModelItens($model_name, $times, $scenario = 'create') {
  $models = array();
  for($i = 0; $i < $times; $i++) { 
    $models[$i]           = new $model_name; 
    $models[$i]->scenario = $scenario;
  }
  return $models;
}
private function validateModels($forms, $models) {
  $valid  = true;
  foreach($forms as $k => $form) { 
    $models[$k]->attributes = $form;
    $models[$k]->position   = $k;
    $valid = $models[$k]->validate() && $valid;
  }
  return $valid;
}
private function saveModels($models, $company_id) {
  foreach($models as $k => $model) {
    $model->company_id = $company_id;
    if($model instanceOf File) {
      if($model->save()) $this->upload_file($model, "file"); 
    } else $model->save();
  }
}

private function upload_file($model, $field, $k) {
  $path = Yii::app()->basePath . "/../assets/files/companies/{$model->company_id}/";
  $file = CUploadedFile::getInstance($model, $field);
  if($file instanceof CUploadedFile) $model->$field = $file;
  if($model->$field instanceof CUploadedFile) {
    if(!file_exists($path)) exec("mkdir -p {$path}");
    $model->$field->saveAs($path . $model->$field);
  }
}

我已经尝试了所有的方法，但是我不能解决它，有什么建议吗?

谢谢。