On Sat, Aug 21, 2010 at 8:09 AM, Andy <selforgani...@gmail.com> wrote: >
> So is there any way to write the database router to route the above > query? Other than explicitly naming the database -- not at present. Of course, given that you know your sharding scheme, you could use the router directly. Tweet.objects.using(router.db_for_read(Tweet, author=a)).filter(author_id=a) This will use the router to determine the right database, based upon a custom 'author' hint. It will require a bit of extra logic in your router, and a little extra work whenever you use the Tweet object., but it will ensure your routing logic is used consistently. >> If you think that Django isn't providing >> sufficient information to implement a specific routing scheme, make >> your case and we will see about adding whatever extra information may >> be required. > > The issue with using only "instance" as a hint is that in almost all > cases of database reads there isn't any instance to speak of at the > time the query is being issued. After all the very purpose of a > database read is to retrieve the instance! No - the purposes of a database read is to issue queries, which may represent an instance, or many instances, or selected columns from one or many instances, or aggregated data across instances. The filter clause *might* include the argument being used as a sharding deteminant, or it might not; it might be a simple equality query, or it might be a gt/lt/not clause; and the sharding behavior that is implemented may be based on a combination of multiple factors, rather than a single field value. As always, the devil is in the detail. > The above example of: > Tweet.objects.filter(author_id=123) > represents pretty much the most common scenario for database sharding. > I'd think it's important for Django's multidatabase function to be > able to handle a case like that. You won't get any argument from me. What's missing is a clear suggestion on how we can encompass this problem in the general case. Suggestions are welcome. Yours, Russ Magee %-) -- 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.
