ManyToManyField多个模型之间的关系 [英] ManyToManyField Relationships Between Multiple Models

问题描述

我有以下代表书籍和作者的模特儿。一本书可以有多个作者，作者可以编写多本书。所以我使用Django的 ManyToManyField 类型将两个模型相互链接。

我可以使用Django管理员添加一个书，并创建一个作者。但是当我查看作者时，我刚刚创建它没有链接到书。我必须明确地设置作者实例和书实例之间的反向关系。

这是正是或者我可以做不同的事情吗？

Models.py

  class Book（models.Model）：
 book_title = models.CharField（max_length = 255，blank = False）
 authors = models.ManyToManyField （'作者'，空白=真）
 
类作者（models.Model）：
 author_first_name = models.CharField（max_length = 255，blank = False）
 author_last_name = models .CharField（max_length = 255，blank = False）
 books = models.ManyToManyField（Book，blank = True）
  

解决方案

您不需要两个 ManyToManyField 定义，因为模型类没有 ManyToManyField 通过相反的关系与另一个相关。请参阅： https：//docs.djangoproject。 com / en / dev / topics / db / queries /＃many-to-many-relationships

如果将两个模型类定义为： p>

  class Book（models.Model）：
 book_title = models.CharField（max_length = 255，blank = False）
 authors = models.ManyToManyField（'Author'，blank = True）
 
类作者（models.Model）：
 author_first_name = models.CharField（max_length = 255，blank = False） 
 author_last_name = models.CharField（max_length = 255，blank = False）
  

然后为任何作者实例 a ， a.book_set.all（）由作者撰写（或共同撰写）的书籍组成。

I have the following models that represent books and authors. A single book can have multiple authors and an author could have written multiple books. So I am using Django's ManyToManyField type to link the two models to each other.

I can add a Book, using the Django Admin perhaps, and create an Author in the process. But when I view the Author I just created it's not linked to the Book. I have to explicitly set the reverse relationship between the Author instance and the Book instance.

Is that just the way it is or could I be doing something different?

Models.py

class Book(models.Model):    
    book_title = models.CharField(max_length=255, blank=False)
    authors = models.ManyToManyField('Author', blank=True)

class Author(models.Model):
    author_first_name = models.CharField(max_length=255, blank=False)
    author_last_name = models.CharField(max_length=255, blank=False)
    books = models.ManyToManyField(Book, blank=True)

解决方案

You don't need two ManyToManyField definitions because the model class without the ManyToManyField is related to the other through the reverse relationship. See: https://docs.djangoproject.com/en/dev/topics/db/queries/#many-to-many-relationships

If you defined the two model classes as:

class Book(models.Model):    
    book_title = models.CharField(max_length=255, blank=False)
    authors = models.ManyToManyField('Author', blank=True)

class Author(models.Model):
    author_first_name = models.CharField(max_length=255, blank=False)
    author_last_name = models.CharField(max_length=255, blank=False)

then for any Author instance a, a.book_set.all() consists of the books that the author wrote (or co-wrote).

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