How do I query foreign key relationships in Django?

How do I query foreign key relationships in Django?

In Django, you can query foreign key relationships using the related name or the model name followed by the field name. For example, if you have a model Book with a foreign key to Author, you can access the books of an author using author.book_set.all().

Can you give me an example of how to filter results based on a foreign key?

Sure! If you want to filter books by a specific author, you can do something like this: Book.objects.filter(author__name='John Doe'). This will return all books written by 'John Doe'.

What if I want to get authors who have written more than one book?

You can use the annotate and filter methods together. For example: Author.objects.annotate(num_books=Count('book')).filter(num_books__gt=1) will give you authors with more than one book.

Is there a way to order the results by the number of books?

Yes! You can order the results by the annotated count like this: Author.objects.annotate(num_books=Count('book')).order_by('-num_books') to get authors sorted by the number of books in descending order.