[英]django get queryset of a object with chained foreign key
我有一個看起來像這樣的項目:
mysite/
|-- books
| |-- __init__.py
| `-- models.py
`-- org
|-- __init__.py
`-- models.py
書籍/ models.py:
from django.db import models
from mysite.org.models import Team
class BookSet(models.Model):
name = models.CharField(max_length=10)
team = models.ForeignKey(Team, related_name='booksets')
class Book(models.Model):
name = models.CharField(max_length=10)
book_set = models.ForeignKey(BookSet, related_name='books')
組織/ models.py:
from django.db import models
class Department(models.Model):
name = models.CharField(max_length=20)
class Team(models.Model):
name = models.CharField(max_length=20)
department = models.ForeignKey(Department, related_name='teams')
我要實現的是獲取部門的所有書籍,類似於:
class Department(models.Model):
name = models.CharField(max_length=20)
@property
def books(self):
# this won't work, is there any possible do it like this?
return self.teams.booksets.books()
我知道一種可能的方法是通過:
from mysite.books.models import Book
class Department(models.Model):
name = models.CharField(max_length=20)
@property
def books(self):
return Book.objects.filter(book_set__team__department=self)
但是使用這種方法,我需要做一些棘手的事情,以允許它們(books.models和org.models)周期性地相互導入。
因此,我想知道是否可以通過查詢外鍵來查找某個部門的所有書籍,例如:
@property
def books(self):
# this won't work, is there any possible do it like this?
return self.teams.booksets.books()
避免周期性導入的一種簡單方法是使您的Department
模型如下:
class Department(models.Model):
name = models.CharField(max_length=20)
@property
def books(self):
from mysite.books.models import Book
return Book.objects.filter(book_set__team__department=self)
我認為這樣會起作用:
class Department(models.Model):
name = models.CharField(max_length=20)
@property
def books(self):
booksets = list(team.booksets.all() for team in self.teams.all())
return list(bookset.books.all() for bookset in booksets)
但是我沒有簡單的方法來測試它。
編輯:另一種我忘了添加:
您可以使用字符串來引用ForeignKey定義中的模型。 像這樣:
class BookSet(models.Model):
name = models.CharField(max_length=10)
team = models.ForeignKey('org.Team', related_name='booksets')
然后在其他應用程序中,您可以自由導入books.models
有關更多信息,請參閱文檔 。
您可以使用Django用於加載外鍵的相同機制,例如
user = models.ForeignKey('User')
怎么做的:
from django.db.models.loading import get_model
Book = get_model('books', 'Book')
# which would achieve the same thing as
# from books.models import Book
get_model
定義為:
def get_model(self, app_label, model_name, seed_cache=True): ...
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