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class Book(models.Model):
# fields
class Chapter(models.Model):
book = models.ForeignKey(Book)
class Page(models.Model):
chapter = models.ForeignKey(Chapter)
I want all the pages of the book A, possibly without cycling every chapter to fetch the pages.
book = Book.objects.get(pk=1)
pages = book.chapter_set.page_set #?!?
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The related_name attribute specifies the name of the reverse relation from the User model back to your model. If you don't specify a related_name, Django automatically creates one using the name of your model with the suffix _set.
What is ForeignKey in Django? ForeignKey is a Field (which represents a column in a database table), and it's used to create many-to-one relationships within tables. It's a standard practice in relational databases to connect data using ForeignKeys.
The only difference between these two is that ForeignKey field consists of on_delete option along with a model's class because it's used for many-to-one relationships while on the other hand, the OneToOneField, only carries out a one-to-one relationship and requires only the model's class.
One of the most powerful features of Django is its Object-Relational Mapper (ORM), which enables you to interact with your database, like you would with SQL. In fact, Django's ORM is just a pythonical way to create SQL to query and manipulate your database and get results in a pythonic fashion.
You can't do it that way. chapter_set is a query set, it doesn't have an attribute page_set.
Instead, turn it around:
Page.objects.filter(chapter__book=my_book)
When you query cross models, double underscores may help
book = Book.objects.get(pk=1)
pages = Page.objects.filter(chapter__book=book)
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