django - 将回调作为upload_to 传递给FileField

Question

我有一个抽象模型类 UploadItem 用于处理上传的文件。我希望每个子类都能够定义 upload_to 路径。为此，我将回调传递给 FileField 的构造函数。

这是一个例子:

class UploadItem(models.Model):
    file = models.FileField(upload_to=UploadItem.get_directory) 


    class Meta:
        abstract = True
# I want videos to be storred in 'videos/' directory
class Video(UploadItem):
    def get_directory(self, instance, filename):
        return 'videos/'

但这不起作用，我收到此错误:

file = models.FileField(upload_to=UploadItem.get_directory) 
NameError: name 'UploadItem' is not defined

Answer 1

考虑到在评估时，错误是很自然的

file = models.FileField(upload_to=UploadItem.get_directory) 

UploadItem类尚未定义。您可以执行以下操作以使其工作:

def get_directory():
    pass

class UploadItem(models.Model):
    file = models.FileField(upload_to=get_directory)

    class Meta:
        abstract = True

但这并不能解决您所有的问题。添加(或覆盖)方法 get_directory在 Video类不会改变 upload_to file 的属性(property)模型的属性。

更新

documentation说 upload_to可以是一个可调用的。

This may also be a callable, such as a function, which will be called to obtain the upload path, including the filename. This callable must be able to accept two arguments, and return a Unix-style path (with forward slashes) to be passed along to the storage system.

鉴于此，我们可以编写一个自定义回调函数，如下所示:

categories_and_paths = { 'video': 'videos/', 'photo': 'photos/' } # etc.
def get_directory(instance, filename):
    category = instance.category
    return categories_and_paths.get(category, '')

Instance这里将是相应模型的实例。为此，每个模型实例都应该有一个类别字段。我们可以在模型的主体中添加一个。

class Video(UploadItem):
    category = 'video'