Django中metaclass与modelformset_factory的冲突

Question

我正在使用Django的模型继承功能来创建两个模型——WorkAttachmentPicture和WorkAttachmentAudio。

class WorkAttachment(models.Model):
    """ Abstract class that holds all fields that are required in each attachment """
    work            = models.ForeignKey(Work)
    added           = models.DateTimeField(default=datetime.datetime.now)
    views           = models.IntegerField(default=0)

    class Meta:
        abstract = True


class WorkAttachmentFileBased(WorkAttachment):
    """ Another base class, but for file based attachments """
    description     = models.CharField(max_length=500, blank=True)
    size            = models.IntegerField(verbose_name=_('size in bytes'))

    class Meta:
        abstract = True


class WorkAttachmentPicture(WorkAttachmentFileBased):
    """ Picture attached to work """
    image           = models.ImageField(upload_to='works/images', width_field='width', height_field='height')
    width           = models.IntegerField()
    height          = models.IntegerField()

class WorkAttachmentAudio(WorkAttachmentFileBased):
    """ Audio file attached to work """
    file            = models.FileField(upload_to='works/audio')

一个工作可以有多个音频和视频附件，所以我使用modelformset_factory来创建表单：

class ImageAttachmentForm(forms.ModelForm):
    """ Image attached to work """
    image = forms.FileField(
        label=_('File'),
        help_text=_('JPEG, GIF or PNG image.')
    )
    description = forms.CharField(
        widget=forms.Textarea(),
        label=_('File description'),
        help_text=_('Max. 500 symbols.'),
        max_length=500
    )

    class Meta:
        model = WorkAttachmentPicture
        fields = ['image', 'description']

ImageAttachmentFormSet = modelformset_factory(WorkAttachmentPicture, form=ImageAttachmentForm)


class AudioAttachmentForm(forms.Form):
    """ Audio file attached to work """
    file = forms.FileField(
        label=_('File'),
        help_text=_('MP3 file.')
    )
    description = forms.CharField(
        widget=forms.Textarea(),
        label=_('File description'),
        help_text=_('Max. 500 symbols.'),
        max_length=500
    )

    class Meta:
        model = WorkAttachmentAudio
        fields = ['file', 'description']

AudioAttachmentFormSet = modelformset_factory(WorkAttachmentAudio, form=AudioAttachmentForm)

我觉得一切都没问题，但在项目启动时出现了错误：

metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

如果我只创建一个表单集（比如ImageAttachmentFormSet），一切正常。但当我添加另一个表单集时，就会出现错误。我该如何解决这个问题，以便在继承模型中使用表单集呢？

Answer 1

解决了。如果你仔细看看

# this has forms.ModelForm
class ImageAttachmentForm(forms.ModelForm):
# this has forms.Form
class AudioAttachmentForm(forms.Form):

我把 forms.Form 改成了 forms.ModelForm，现在一切都正常了——这只是一个简单的复制粘贴错误。