Re: How to select objects referenced by another table ?
On 17 juil, 20:29, Tim Chase <[EMAIL PROTECTED]> wrote: > Fortunately, Django's ORM lets you get at the underlying SQL via > a call to .extra() where you can provide your own WHERE clause. > This would look something like > >Article.objects.extra(where=""" > app_article.id in (select article_id from app_photo) > """) > > You'd have to adjust for the various column-names and table-names > accordingly. Argl, I missed the 'extra' method in the documentation, thanks a lot ! --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~--~~~~--~~--~--~---
Re: How to select objects referenced by another table ?
> Fortunately, Django's ORM lets you get at the underlying SQL via > a call to .extra() where you can provide your own WHERE clause. > This would look something like > >Article.objects.extra(where=""" > app_article.id in (select article_id from app_photo) > """) Whoops...forgot that where="" takes a list of strings, that should be where=["..."] -tkc --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~--~~~~--~~--~--~---
Re: How to select objects referenced by another table ?
> What I want is "every articles which have at least one photo" > (and the possibility to add more filter after that, > eventually). > > > Currently, I'm using something like : > > Article.objects.filter(photos__in=Photo.objects.all()) > > but this is horribly inefficient, since there is more than > 4 photos in the database You are correct that that's the straightforward way to do it, but as you've discovered, anything more than a handful of Photo objects, and the SQL gets crazy. Fortunately, Django's ORM lets you get at the underlying SQL via a call to .extra() where you can provide your own WHERE clause. This would look something like Article.objects.extra(where=""" app_article.id in (select article_id from app_photo) """) You'd have to adjust for the various column-names and table-names accordingly. This also assumes that you have a one-to-many relationship between photos and articles (a single photo doesn't appear on multiple articles) or otherwise you'd have to adjust the query to go through a joining table. The efficiency of IN vs EXISTS can be debated and really depends on your backend DB, but if you find performance problems, it can be a good place to start your tweaking: where="""EXISTS ( select 1 from app_photo where article_id = app_article.id )""" Hope this helps, -tkc --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~--~~~~--~~--~--~---
How to select objects referenced by another table ?
Hello, I want to create a QuerySet object which select objects from a table which a referenced by another table, but I can't find how to do that. Here is an example : class Article(models.Model): [...] class Photo(models.Model): article = models.ForeignKey(Article) [...] What I want is "every articles which have at least one photo" (and the possibility to add more filter after that, eventually). Currently, I'm using something like : Article.objects.filter(photos__in=Photo.objects.all()) but this is horribly inefficient, since there is more than 4 photos in the database (and PostgreSQL doesn't accept this query either, but this is another problem ...) How can I do that ? Thanks for your answer, - Jonathan --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~--~~~~--~~--~--~---
