On Thu, Apr 11, 2013 at 3:42 PM, Matthieu Bouron <[email protected]> wrote: > Hello, > > Is there a way to handle many-to-many relationship with raw sql queries ? > I have the following model: > > from django.db import models > > class Tag(models.Model): > name = models.CharField(max_length=512, unique=True) > > class Bookmark(models.Model): > link = models.CharField(max_length=512) > title = models.CharField(max_length=512) > tags = models.ManyToManyField(Tag) > added_at = models.DateField() > > Using Bookmark.objetcs.all() will result in a subquery for each row of the > bookmark table which is not acceptable for performance reasons. > First question is there a way to fetch all the content with a single query ? > Second question is it possible to use raw sql queries. I tried the > following: > > bookmarks = Bookmark.objects.raw( > 'SELECT * FROM bookmarkmanager_bookmark b ' > 'LEFT JOIN bookmarkmanager_bookmark_tags bt ON (b.id = > bt.bookmark_id) ' > 'LEFT JOIN bookmarkmanager_tag t ON (bt.tag_id = t.id)' > ) > > But when i tried to access the tags attribute on a bookmark i get the > following exception: > > ValueError: "<Bookmark: Bookmark object>" needs to have a value for field > "bookmark" before this many-to-many relationship can be used. > > Thanks in advance, > Matthieu >
Are you tied to raw SQL queries? Django itself supports traversing M2M relationships in a sane manner if you tell it to do so: https://docs.djangoproject.com/en/1.5/ref/models/querysets/#prefetch-related Cheers Tom -- 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 http://groups.google.com/group/django-users?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
