May you please post the code of Book and Author models? Thanks
Leonardo Giordani Author of The Digital Cat <http://lgiordani.github.com> My profile on About.me <http://about.me/leonardo.giordani> - My GitHub page<https://github.com/lgiordani>- My Coderwall profile <https://coderwall.com/lgiordani> 2013/11/16 J. C. Leitão <jorgecarlei...@gmail.com> > Hi there. > > Consider the situation where you want to order_by a sum of two fields > obtained from an annotation. This > problem<http://stackoverflow.com/questions/4899014/using-extra-on-fields-created-by-annotate-in-django> > states > it correctly, however, the solution is not working for me. > > For concreteness, consider the example: > > Author.objects.annotate(first_date=Avg('all_books__published_date'), > last_date=Avg('all_books__added_date'))\ > .extra(select = {'delta_time': 'last_date - > first_date'}, > order_by=['-delta_time']) > > Where: > > - Book has a manyToMany relationship with Author and 'all_books' is the > related_name from the book to the author. > - *_date are dates. > > I.e. For each author, I'm computing the average time it takes for a book > to be added (e.g. to a library) since the moment it was published. > > This query is not correct as "(1054, "Unknown column 'last_date' in 'field > list'")", which I suspect is because the field all_books is a ManyToMany. > > The > solution<http://stackoverflow.com/questions/4899014/using-extra-on-fields-created-by-annotate-in-django> > I > found so far was an extra like this: > > Author.objects.extra( > select = {'delta_time': 'AVG(all_books__added_date) - > AVG(all_books__published_date)'}, > order_by = ['-delta_time'] > ) > > but in this case this is not working with the error ""Unknown column > 'all_books__added_date'", which I suspect is also because the field is a > ManyToMany. > > Any ideas on how to create this query? > > Thanks, > Jorge > > -- > 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 django-users+unsubscr...@googlegroups.com. > To post to this group, send email to django-users@googlegroups.com. > Visit this group at http://groups.google.com/group/django-users. > To view this discussion on the web visit > https://groups.google.com/d/msgid/django-users/104ab2a3-17e7-4726-be87-0ac353d957ca%40googlegroups.com > . > For more options, visit https://groups.google.com/groups/opt_out. > -- 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 django-users+unsubscr...@googlegroups.com. To post to this group, send email to django-users@googlegroups.com. Visit this group at http://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/CAEhE%2BOk4ey8b3Opt32K082r%3Drr%2BFnH0Ne4QnyCUxRiB7dgW9Wg%40mail.gmail.com. For more options, visit https://groups.google.com/groups/opt_out.
