On Thursday, April 11, 2013 5:39:57 PM UTC+2, Tom Evans wrote: > > On Thu, Apr 11, 2013 at 3:42 PM, Matthieu Bouron > <[email protected] <javascript:>> 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 >
Thanks. Another problem remains ... performances are horrible even if i use values(). I have 1000 rows in base, executing from a script (db sqlite): - 800ms to fetch all the objects (traversing m2m with prefetch_related). - 200ms to fetch all the row from bookmark table without traversing the m2m relationship). Are my results expected ? Are there any plan on improving django orm performance ? Matthieu -- 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.
