如何从Django的模块中的给定字段中获取所有引用为ForeignKey的对象 [英] How to get all objects referenced as ForeignKey from given field in a module in django

问题描述

我有两个班：作者和书。我希望类作者具有一个属性，该属性包含由该作者编写的所有书籍，作为类Books中的外键引用。我采用的方法似乎无效，我认为这是因为在迁移中创建数据库时，还没有Books对象。

  class Author（models.Model）：
 AuthorName = models.CharField（max_length = 255，unique = True）
 books = Book.objects.get（pk = object_instance.pk）
 
 class Book（models.Model）：
 BookName = models.CharField（max_length = 255）
 Author = models.ForeignKey（'Author'）
  

我得到的错误消息是：

  NameError：未定义名称'Book'
  

我得到的是，因为我引用的是另一个类，而实际上并没有该类的实例。我只是不知道执行此操作的正确方法。

编辑：我将其重新格式化为如下格式：

 类Author（models.Model）：
 AuthorName = models.CharField（max_length = 255，unique = True）
 books = author.book_set.all （）
 
 class Book（models.Model）：
 BookName = models.CharField（max_length = 255）
 Author = models.ForeignKey（'Author'）
  

这会产生错误：

  NameError：未定义名称作者 
  

也许我应该只查询数据点

编辑2：答案的解决方案：

所以我一直以来的错误是尝试在author表中添加 books字段。我想那时没有办法了。我可以让该方法在视图中工作，所以我认为这已经解决了，尽管不是我最初计划的方式。

这样做

  class Author（models.Model）：
 AuthorName = models.CharField（max_length = 255，unique = True）
 
 class Book（models.Model）：
 BookName = models.CharField（max_length = 255）
 Author = models.ForeignKey（'Author'）
  

，然后在视图中执行此操作：

  author = Author.objects.get（pk = 1）
 books = author.book_get.all（）
  

产生所需的结果（我之前已经知道这一点，但是我试图在模型中实现一个book字段，如果我正确理解的话，至少使用这种方法是不可能的）。 / p>

另一个解决方案：

  class Author（models.Model）：
 AuthorName = models.CharField（max_length = 255，unique = True）
 
 class Book（mo dels.Model）：
 BookName = models.CharField（max_length = 255）
 Author = models.ForeignKey（Author，related_name = books）
  

解决方案

您无需在作者模型

  class Author（models.Model）：
 AuthorName = models.CharField（max_length = 255，unique = True）
 
 class Book（models.Model）：
 BookName = models.CharField（max_length = 255）
 Author = models.ForeignKey（'Author'）
  

您可以获取特定作者的所有书籍，例如：

  author = Author.objects.get（id = 1）
图书= author.book_set.all（）
  

了解有关向后关系的更多信息此处

I have two classes: Author and Book. I want class Authors to have an attribute that contains all books written by the said author, as referenced to as foreign key in the class Books. The method I did does not appear to be working, which I assume is because when the database is being created in migrations, no Books objects exist yet. Or so I believe, I'm pretty new at django.

class Author(models.Model):
    AuthorName = models.CharField(max_length=255, unique=True)
    books = Book.objects.get(pk=object_instance.pk)

class Book(models.Model):
    BookName = models.CharField(max_length=255)
    Author = models.ForeignKey('Author')

The error message I get is:

NameError: name 'Book' is not defined

Which I get, is because I'm referencing to another class without actually having and instance of that class. I just can't figure out a proper way to do this.

EDIT: I reformatted it to be like this:

class Author(models.Model):
    AuthorName = models.CharField(max_length=255, unique=True)
    books = author.book_set.all()

class Book(models.Model):
    BookName = models.CharField(max_length=255)
    Author = models.ForeignKey('Author')

which yields error:

NameError: name 'author' is not defined

Maybe I should just query for the datapoints I need later on in views as opposed to creating own field for them in models though..

EDIT 2: solution from answers:

So my mistake all along was to try to add the "books" field in the author table. I guess there's no way to do this then. I can get that method to work in views so I guess this is sort of solved, although not in the way I was originally planning to do it.

doing

class Author(models.Model):
    AuthorName = models.CharField(max_length=255, unique=True)

class Book(models.Model):
    BookName = models.CharField(max_length=255)
    Author = models.ForeignKey('Author')

and then later doing this in views:

author = Author.objects.get(pk=1)
books = author.book_get.all()

yields the wanted result (which I sort of knew beforehand, but I was trying to implement a books field in the models, which, if i correctly understood, is not possible at least not with this method).

another solution:

class Author(models.Model):
    AuthorName = models.CharField(max_length=255, unique=True)

class Book(models.Model):
    BookName = models.CharField(max_length=255)
    Author = models.ForeignKey(Author, related_name = "books")

解决方案

You don't need to create a separate field in Authors model

class Author(models.Model):
    AuthorName = models.CharField(max_length=255, unique=True)

class Book(models.Model):
    BookName = models.CharField(max_length=255)
    Author = models.ForeignKey('Author')

You can get all books of a particular author like:

author = Author.objects.get(id=1)
books = author.book_set.all()

Learn more about backward relationships here

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