定义默认子级（反向ForeignKey）

发布于 2024-12-01 12:46:06 字数 461 浏览 1 评论 0原文

我有 2 个模型 Foo 和 Bar。每个 Foo 都有多个 Bar，但其中一个需要是“默认”的。此时，Bar 中有一个指向 Foo 的外键，但现在我需要一种方法来指定属于 Foo 的 Bar 中的哪个是默认值。我尝试在 Foo 中设置另一个指向 Bar （具有唯一的 related_name ）的外键，但出现各种错误（包括在 django-admin 模板中）。

到目前为止的代码：

class Foo(models.Model):
    default_bar = models.ForeignKey('Bar')

class Bar(models.Model):
    foo = models.ForeignKey(Foo)

我对全新的解决方案绝对没有问题，因为无论如何我可能都做错了。我能想到的唯一的其他方法是有一个单独的表来连接 Foos 和 Bars 并使 Foo 部分唯一，但这使得管理界面变得混乱。

原文

I have 2 models Foo and Bar. Each Foo has multiple Bars, but one needs to be the "default". At this point I have a foreignkey in Bar pointing to Foo, but now I need a way to specify which of the Bar's belonging to Foo is the default. I tried setting another foreignkey in Foo that points to a Bar (with a unique related_name), but I get all sorts of errors (including in the django-admin templates).

Code so far:

class Foo(models.Model):
    default_bar = models.ForeignKey('Bar')

class Bar(models.Model):
    foo = models.ForeignKey(Foo)

I have absolutely NO problem with a completely new solution as I'm probably doing it wrong anyways. The only other way I can think of is to have a separate table that connects Foos and Bars and having the Foo part unique, but that makes the admin interface a MESS.

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情话难免假 2024-12-08 12:46:06

如果一个Foo可以有多个Bar，那么一个Bar可以属于多个Foo吗？如果是这样，那么您可以使用 ManyToManyField 和 through 参数轻松解决此问题，如下所示：

class Foo(models.Model):
    name = models.CharField(max_length=128)
    bars = models.ManyToManyField(Bar, through='FooBar')

class Bar(models.Model):
    name = models.CharField(max_length=128)

class FooBar(models.Model):
    foo = models.ForeignKey(Foo)
    bar = models.ForeignKey(Bar)
    is_default = models.BooleanField()

查看 Django 文档 "多对多关系上的额外字段" 。

作为注释，发布您实际问题的简单版本（即说 Person 和 Group 与 Foo 和 Bar）会有所帮助，因为我们可以更好地了解您实际尝试建模的内容！这样就可以更容易地了解关系实际上应该走向何方。

If a Foo can have multiple Bars, then can a Bar belong to multiple Foos? If so then you can solve this really easily with a ManyToManyField and the through parameter, like this:

class Foo(models.Model):
    name = models.CharField(max_length=128)
    bars = models.ManyToManyField(Bar, through='FooBar')

class Bar(models.Model):
    name = models.CharField(max_length=128)

class FooBar(models.Model):
    foo = models.ForeignKey(Foo)
    bar = models.ForeignKey(Bar)
    is_default = models.BooleanField()

Check the Django documentation on "Extra fields on many-to-many relationships".

And just as a note, posting a simple version of your actual problem (ie. saying Person and Group vs. Foo and Bar) helps, as we get a better understanding of what you're actually trying to model! That way it's easier to see where the relationships should actually go.

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