Django：维护单独的对象集，几乎就像“孩子”一样
我目前正在掌握 Django 的一些优点，并开始认真使用它。我有一个示例，其中有一些外键关系，并且我想将对象分开。这是一个快速的 models.py 示例：
class CopyOfBook(models.Model):
barcode = models.CharField(max_length=100)
class Book(models.Model):
title = models.CharField(max_length=100)
copies = models.ManyToManyField(CopyOfBook)
class Library(models.Model):
name = models.CharField(max_length=100)
books = models.ManyToManyField(Book)
每个组件都依赖于其父组件 - 例如，一本书不能存在于库之外，并且特定于单个库。我知道这是一个稍微做作的示例，但是在 Django 中对此进行建模的最佳方法是什么？
问题是，如果您打开管理并添加一本新书，您将看到所有 CopyOfBook 实例的列表，而不仅仅是属于该书的实例（当添加新书时，将是一个空列表）。
希望我已经解释得足够清楚了，如果您需要任何说明，请告诉我。
更新：我一直在尝试使用ManyToMany.limit_choices_to，并在参数中使用适当的lated_name，但没有太多乐趣。
I'm currently getting to grips with some of the finer points in Django, and I'm beginning to use it in earnest. I've got an example where I have a few foreign key relationships, and I want to keep the objects separate. Here's a quick models.py example:
class CopyOfBook(models.Model):
barcode = models.CharField(max_length=100)
class Book(models.Model):
title = models.CharField(max_length=100)
copies = models.ManyToManyField(CopyOfBook)
class Library(models.Model):
name = models.CharField(max_length=100)
books = models.ManyToManyField(Book)
Each of those components depends on its parent - for example, a Book can't exist outside of a Library, and is specific to a single library. I know it's a slightly contrived example, but what's the best way to model this in Django?
The problem is, that if you opened up the admin and added a new Book, you'd be presented with a list of all the CopyOfBook instances, rather than just those that belong to that book (which when adding a new one, would be an empty list).
Hopefully I've explained that clearly enough, let me know if you need any clarification.
Update: I have been trying to use ManyToMany.limit_choices_to, and using the appropriate related_name in the arguments, but without much joy.
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您应该首先考虑您的实体关系模型。
CopyOfBook 有一个书和一个库。所以你可以给每个它一个外键。
Book 和 Library 仅通过 CopyOfBook 连接。因此，虽然这不是绝对必要的（上面两个外键就足够了），但您可以使用 through=CopyOfBook 为 Library 提供与 Book 的多对多关系。
You should start by thinking of your entity-relationship model.
A CopyOfBook has a single Book and a single Library. So you can give it a ForeignKey to each.
Book and Library are only connected through a CopyOfBook. So while this isn't strictly necessary (the two above ForeignKey suffice), you can give Library a ManyToMany relationship to Book with through=CopyOfBook.
如果一本书特定于单个库，您应该在其上添加一个
ForeignKey到 Library，而不是在Library中添加一个ManyToManyField。另外，我认为CopyOfBook也将特定于一本书，所以这同样适用于这里！然后，您可以通过 InlineModelAdmins 管理书籍和副本！
If a book is specific to a SINGLE library you should rather have a
ForeignKeyto Library on it, than aManyToManyFieldinLibrary. Also I suppose aCopyOfBookwill also be specific for a single book, so the same applies here!You could then administrate the books and copies via InlineModelAdmins!
Library和Book之间的ManyToMany关系很好，因为多个图书馆可以拥有同一本书。但是，Book和CopyOfBook之间的ManyToMany关系对我来说没有意义。特定副本可以是特定书籍的。相反，您应该拥有一种多对一 (ForeignKey)关系，它将一本特定的书与其多个副本相关联。The
ManyToManyrelationship that you have betweenLibraryandBookis fine, because more than one library can have the same book. However, theManyToManyrelationship that you have betweenBookandCopyOfBookdoes not make sense to me. A particular copy can be of a particular book. What you should have there instead is amany-to-one (ForeignKey)relationship, which will associate a particular book with more than one copies of it.