Yes, this conversation hits the nail on the head. 'select related' only works with forward facing keys.
http://code.google.com/p/django-selectreverse/ is a resonably good piece of code to improve performance: using a structure like: class model1(model.Models) 1<----* class model2(model.Models) model1 = models.foreignkey(model1) 1<----* class model3(model.Models) model1 = models.foreignkey(model1) etc... where your view/template code is: for x in model1.objects.all() #stuff for y in x.model2_set.all() #stuff for y in x.model3_set.all() #stuff Gets awfully slow as you add modelX_set.all or scale it up to thousands of rows. eg: where model1 is 945 rows in the sql db: time taken: 1.023 SQL queries: 1883 using select related: time taken: 0.493 SQL queries: 21 I have not tried select related performance where there may be another model with a reverse foreignkey facing model2. I don't know how well it will face a multi level reverse foreign key/many to many db structure. Also don't forget to look at indexing for certain fields where appropriate it can be a good performance improver: http://docs.djangoproject.com/en/1.1/ref/models/fields/#db-index cheers sam_w On Fri, Mar 19, 2010 at 5:15 AM, koenb <koen.bierm...@werk.belgie.be> wrote: > On 18 mrt, 10:12, bruno desthuilliers <bruno.desthuilli...@gmail.com> > wrote: >> On Mar 18, 8:42 am, koenb <koen.bierm...@werk.belgie.be> wrote: >> >> > Take a look at something like django-selectreverse [1] for inspiration >> > on how to reduce your querycount for M2M relations. >> >> > Koen >> >> > [1]http://code.google.com/p/django-selectreverse/ >> >> I must be missing the point, but it looks seriously like reinventing >> the wheel ? How is it better than using select_related ??? > > Select_related only populates forward one-to-many relationships > (foreignkeys). > It does not work for many-to-many relationships or reverse one-to-many > relationships (the XX_set descriptors on the other side of fk's). > You can not load those in one and the same query, but you can load all > those objects in one single query instead of N extra queries. > That is what selectreverse helps you to do. Look at the example on the > introduction page of the project to see what kind of queries I mean. > > Koen > > -- > You received this message because you are subscribed to the Google Groups > "Django users" group. > To post to this group, send email to django-us...@googlegroups.com. > To unsubscribe from this group, send email to > django-users+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/django-users?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-us...@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
