Python 如何在 Django 的模板中获取模型的对象计数？
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How can I get the object count for a model in Django's templates?
提问by Mridang Agarwalla
I'm my Django application I'm fetching all the objects for a particular model like so:
我是我的 Django 应用程序，我正在为特定模型获取所有对象，如下所示：
secs = Sections.objects.filter(order__gt = 5)
I pass this varbiles to my templates and i can access all the properties of the Model like section.name, section.id, etc.
我通过这个varbiles到我的模板，我可以访问该模型的所有属性，如section.name，section.id等。
There is a model called Bookswhich has a FK to the Sectionsmodel. When i iterate over the secsvarible in my template, how can i access the count of Books for each Section? Something like {{ sec.Books.count }}??
有一个称为模型的模型Books，该Sections模型具有该模型的 FK 。当我遍历secs模板中的变量时，如何访问每个部分的书籍数量？之类的{{ sec.Books.count }}？？
Thank you
谢谢
采纳答案by Daniel Roseman
If Bookshas a ForeignKey to Sections, then Django will automatically create a reverse relationship from Sections back to Books, which will be called books_set. This is a Manager, which means you can use .filter(), .get()and .count()on it - and you can use these in your template.
如果Books有一个 ForeignKey to Sections，那么 Django 会自动创建一个从 Sections 回到 Books 的反向关系，这将被称为books_set。这是一个管理者，你可以使用的手段.filter()，.get()并.count()在其上-你可以在你的模板中使用这些。
{{ sec.books_set.count }}
(By the way, you should use singular nouns for your model names, not plurals - Bookinstead of Books. An instance of that model holds information for one book, not many.)
（顺便说一句，您应该为模型名称使用单数名词，而不是复数 -Book而不是Books。该模型的一个实例包含一本书的信息，而不是很多。）
回答by Mbuso
Additionally to what Daniel said, Django creates reverse relationships automatically (as Daniel said above) unless you override their names with the related_name argument. In your particular case, you would have something like:
除了 Daniel 所说的之外，Django 会自动创建反向关系（如 Daniel 上面所说），除非您使用 related_name 参数覆盖它们的名称。在您的特定情况下，您会有类似的东西：
class Book(models.Model):
section = models.ForeignKey(Section, related_name="books")
Then you can access the section's books count in the template by:
然后，您可以通过以下方式访问模板中该部分的图书计数：
{{ sec.books.count }}
As you intimated in your question.
正如您在问题中所暗示的那样。
回答by Ramy M. Mousa
As for a 2019answer. I would suggest making use of related_namewhile making your ForeignKeyto look like that:
至于2019年的答案。我建议related_name在使您ForeignKey看起来像这样的同时使用：
section = models.ForeignKey(Section, on_delete=models.SET_NULL, related_name='books')
Then you can use it as follows:
然后您可以按如下方式使用它：
{{ section.books.count }}
or
或者
{{ section.books|length }}
