On Apr 18, 1:26 am, koranthala <koranth...@gmail.com> wrote:
> On Apr 18, 1:08 am, Alex Gaynor <alex.gay...@gmail.com> wrote:
>
>
>
> > On Fri, Apr 17, 2009 at 4:05 PM, koranthala <koranth...@gmail.com> wrote:
>
> > > On Apr 17, 11:57 pm, koranthala <koranth...@gmail.com> wrote:
> > > > On Apr 17, 11:51 pm, Alex Gaynor <alex.gay...@gmail.com> wrote:
>
> > > > > On Fri, Apr 17, 2009 at 2:47 PM, koranthala <koranth...@gmail.com>
> > > wrote:
>
> > > > > > Hi,
> > > > > > I am facing a problem which I believe should be a usual issue for
> > > > > > everyone. But I cannot find a way to do it in a straightforward
> > > > > > manner.
> > > > > > I have to select a list of items from table A and delete everyone
> > > > > > of them. Now, there are close to 20K elements which I want to
> > > > > > delete.
> > > > > > So, what I do now is:
> > > > > > fields = tableA.filter(******)
> > > > > > for field in fields:
> > > > > > field.delete()
>
> > > > > > Now, this is invoking 20K separate messages to the DB - which is
> > > > > > rather suboptimal. However I think, I could not find a mechanism to
> > > > > > delete it in a straightway. One option I could think of is to create
> > > > > > raw SQL and invoke - but I would like to do that as the last resort.
> > > > > > Is there any other mechanism to do the same?
>
> > > > > tableA.objects.filter(...).delete()
>
> > > > > Won't pull in each of the objects to delete them:
> > >http://docs.djangoproject.com/en/dev/topics/db/queries/#topics-db-que...
>
> > > > > Alex
> > > > > --
> > > > > "I disapprove of what you say, but I will defend to the death your
> > > right to
> > > > > say it." --Voltaire
> > > > > "The people's good is the highest law."--Cicero
>
> > > > Thank you Alex.
>
> > > Sorry for troubling everyone further. But, I had a similar case of
> > > insert too - wherein I insert close to 2K elements at a time.
> > > Currently, I do it as
> > > list = []
> > > ...
> > > in some loop
> > > ...
> > > table = Table(values)
> > > list.append(table)
> > > ...
>
> > > for l in list: l.save()
>
> > > Is there something similar to block delete - for block insert too?
>
> > Not right now there isn't no(although you don't need the intermediary list,
> > just save the items in the original loop, it will still do 2k queries, but
> > you won't be using a lot of memory storing 2k items). There is a ticket
> > requesting a bulk insert, however I can't seem to find it now.
>
> > Alex
>
> > --
> > "I disapprove of what you say, but I will defend to the death your right to
> > say it." --Voltaire
> > "The people's good is the highest law."--Cicero
>
> Thank you very much Alex.
Again, sorry for troubling you like this.
As I mentioned earlier in this chain, I wanted to delete 20K tuples
from table A.
I am now using tableA.filter(***).delete() to do the same.
Now, table A is referenced by table B - and those need to be deleted
too - via cascade.
What is happening is that - Django is actually sending a query to
table B for each tuple in table A to find out tuples to delete in
table B.
So, I get 20K queries for table B, and 2 delete queries for table A
and B each.
I was wondering whether Django does not support - ON DELETE CASCADE -
in this thread
http://groups.google.com/group/django-users/browse_thread/thread/51f93c9596f9ecd9/9c671e8d16e99b90,
it says it does not support it.
I understand it is done because all backends does not support it - but
can it be supported for backends which actually support it? I am using
postgresql - and now I have to do many non-optimal things to decrease
this query count.
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