Django models.py循环外键 [英] Django models.py Circular Foreign Key

问题描述

我有一个django应用程序，它基本上只是一张相册。现在我有两个模型：图像和相册。除了别的以外，每个相册有一个外键，一个 Image 成为它的缩略图，每个图像具有它所属的相册的外键。但是，当我尝试使用 manage.py syncdb 或 manage.py sqlall 我收到的错误说，在第一类使用时，没有定义在models.py中没有定义的类

models.py（abridged）：

  from django .db导入模型
 import os 
 
 class Album（models.Model）：
 thumb = models.ForeignKey（Image，null = True，blank = True）
 
 class Image（models.Model）：
 image = models.ImageField（upload_to ='t_pics / images'）
 thumb = models.ImageField（upload_to ='t_pics / images / thumbs'） 
 album = models.ForeignKey（Album）
  

$ c> manage.py sqlall appname ：

  [...] 
文件/路径/到/文件/应用程序的名字/ models.py，第4行，在？ 
 class Album（models.Model）：
文件/path/to/file/appname/models.py，第5行，专辑
 thumb = models.ForeignKey（Image，null = True，blank = True）
 NameError：name'Image'未定义
  

我当我在models.py中切换类的顺序时，得到相同的错误，除了它说'Album'undefined 而不是'Image'undefined 我还尝试评论第一类的依赖关系，然后在其他所有内容成功导入后取消注释，但没有帮助。我该如何去做这项工作？我不愿意做一个完整的三等课程 Thumb ，因为它将有很多相同的代码 Image I '也很确定我可以手动将外键添加到数据库，但我希望这是干净而不是黑客。

解决方案

你实际上没有循环引用;问题是，在您定义相册时，您尚未定义图像。您可以使用字符串来修复：

  class Album（models.model）：
 thumb = models。 ForeignKey（'Image'，null = True，blank = True）
  

然而，在这种情况下，你可能需要使用 OneToOneField 而不是外键。 （请注意，您仍然必须使用该字符串的技巧）。

I have a django app which basically is just a photo album. Right now I have two models: Image and Album. Among other things, each Album has a foreign key to an Image to be its thumbnail and each Image has a foreign key to the Album it belongs in. However, when I try to use manage.py syncdb or manage.py sqlall I get errors saying the class not defined first in models.py isn't defined when it is used in the first class defined.

models.py (abridged):

from django.db import models
import os

class Album(models.Model):
    thumb = models.ForeignKey(Image, null=True, blank=True)

class Image(models.Model):
    image = models.ImageField(upload_to='t_pics/images')
    thumb = models.ImageField(upload_to='t_pics/images/thumbs')
    album = models.ForeignKey(Album)

Error I get when I do manage.py sqlall appname:

[...]
 File "/path/to/file/appname/models.py", line 4, in ?
    class Album(models.Model):
  File "/path/to/file/appname/models.py", line 5, in Album
    thumb = models.ForeignKey(Image, null=True, blank=True)
NameError: name 'Image' is not defined

I get the same error when I switch the order of the classes in models.py except it says 'Album' undefined instead of 'Image' undefined I also tried commenting the dependancy in the first class then uncommenting after everything else was successfully imported but that didn't help. How should I go about making this work? I'm reluctant to make an entire third class Thumb because it will have a lot of the same code as Image I'm also pretty sure I could manually add the foreign key to the database but I want this to be clean and not hackish.

解决方案

You don't actually have a circular reference; the issue is that, at the time you define Album, you haven't defined Image yet. You can fix that by using a string instead:

class Album(models.model):
  thumb = models.ForeignKey('Image', null=True, blank=True)

However, in this case, you might want to use a OneToOneField instead of a foreign key. (Note that you'll still have to use the trick with the string, though).

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