Symfony2：如何检查文件输入是否为空

Question

我正在制作一个表单来编辑用户可以上传文件的实体。当他进行一些编辑时，我想检查他是否上传了另一个文件以了解我是否必须删除另一个。我找不到如何知道输入文件是否为空。我怎么能这样做？

Answer 1

public function upload()
{
    if (null === $this->file) {
      // this is the condition where you can get to know that the value of
      // input field is null or not
    }

    // if there is an error when moving the file, an exception will
    // be automatically thrown by move(). This will properly prevent
    // the entity from being persisted to the database on error
    $this->file->move($this->getUploadRootDir(), $this->path);

    unset($this->file);
}

检查symfony documentation