Ah, that totally skipped my mind. Thanks yet once again, Tim! :-)
Best, Ankush On Wednesday, June 29, 2016 at 7:18:31 AM UTC+5:30, Tim Graham wrote: > > 'book' (the model name) is the default value of ForeignKey.related_name > for the publisher field on Book. > > class Book(models.Model): > publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE) > > > https://docs.djangoproject.com/en/stable/ref/models/fields/#django.db.models.ForeignKey.related_name > > On Saturday, June 25, 2016 at 10:11:44 AM UTC-4, Ankush Thakur wrote: >> >> On this page https://docs.djangoproject.com/en/1.9/topics/db/aggregation/ >> we have the following example of aggregation: >> >> # All the following queries involve traversing the Book<->Publisher >> # foreign key relationship backwards. >> >> # Each publisher, each with a count of books as a "num_books" attribute. >> >>> from django.db.models import Count >> >>> pubs = Publisher.objects.annotate(num_books=Count('book')) >> >>> pubs >> [<Publisher BaloneyPress>, <Publisher SalamiPress>, ...] >> >>> pubs[0].num_books >> 73 >> >> The models used in this are as follows: >> >> from django.db import models >> >> class Author(models.Model): >> name = models.CharField(max_length=100) >> age = models.IntegerField() >> >> class Publisher(models.Model): >> name = models.CharField(max_length=300) >> num_awards = models.IntegerField() >> >> class Book(models.Model): >> name = models.CharField(max_length=300) >> pages = models.IntegerField() >> price = models.DecimalField(max_digits=10, decimal_places=2) >> rating = models.FloatField() >> authors = models.ManyToManyField(Author) >> publisher = models.ForeignKey(Publisher) >> pubdate = models.DateField() >> >> class Store(models.Model): >> name = models.CharField(max_length=300) >> books = models.ManyToManyField(Book) >> registered_users = models.PositiveIntegerField() >> >> My question is: How come something like >> "Publisher.objects.annotate(num_books=Count('book'))" work? The name "book" >> is not defined as a reverse relationship (I think it should be accessible >> by "book_set"). >> >> How is this traversal working? >> >> >> Regards, >> Ankush Thakur >> > -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/cd9a9b34-6952-41b6-98db-5f65f6e3cc62%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
