[Chicago] 2 unique keys in a python dict?

[Massimo Di Pierro]

I do not want to insist but I did not get an answer.

How do I write a query in the Django ORM that generates something like  
"SELECT SUM(....) ... GROUP BY ..." without using SQL explicitly?

I need an example in Django. There is nothing in the Django  
documentation.

I know how to do this with other ORMs, I know how to do this without  
an ORM and I know how to do this in Django by looping explicitly.

I just do not know how to use GROUP BY and how to use SUM in Django.

I would like to show it to my class but I do not know how to do it.

Massimo

P.S. Incidentally I know how to do in postscript (as you suggest), in  
fact I did create this library for drawing in postscript (and yes,  
this is stupid, but 12 years ago it seemed like a good idea):

http://bazaar.launchpad.net/%7Emdipierro/qcd/development/annotate/1?file_id=mdp_postscript.h-20080712184703-6ns7zn7nw2d95ete-191




On Oct 9, 2008, at 7:10 PM, Martin Maney wrote:

> On Thu, Oct 09, 2008 at 04:16:00PM -0500, Massimo Di Pierro wrote:
>> I am not suggesting using a web framework. I suggested using a DB +
>> python based database abstraction layer (I do my examples in web2py
>> because that is what I know best).
>>
>> Lukasz said that, in fact, he is using SQLAlchemy.
>
> As we will see, I think either is silly overuse of complex tools for a
> trivial job.  Unless the sheer size of the (unsorted) input to be
> processed is huge, which I don't recall.
>
>> Since Garrett mentioned Django (I did not) and I am not aware of  
>> how to
>> use GROUP BY in Django, the conversation sidetracked.
>
> Oh, is that how it went?  I came across this thread after it was  
> mostly
> done, I guess, and only vaguely remember what I took to be a very
> tongue in cheek mention of Django - you know, the obligatory "...or  
> you
> could use <hot thing that's got all the buzz>" mention.
>
>> My question still stands. How would I do a GROUP BY and a SUM of the
>> grouped records in using Django without multiple queries?
>>
>> I would honestly like to learn that.
>>
>> Do you know?
>
> I have to peel this onion in stages.
>
> First layer: for the problem as originally stated, I'd use the CSV
> library and some IMO trivial Python code (it's possible it's not quite
> as simple as I imagine - from something more recent I'm not sure we've
> actually got the full picture of what needs to be done in the end).
>
> Second layer: if I were required to solve that problem using Django,
> I'd import csv and proceed as above after whatever minimal Djangoness
> requirement had been satisfied.
>
> Third layer: if I had to solve the variant you seem to be asking for
> above - assuming the raw records were already in a table by whatever
> means - I, personally, would write a single SQL query, as this is
> pretty trivial (well, after all, subtotals on a field are surely among
> the common business tasks the designers of SQL had in mind).  This
> exposes my bias as someone who had taken the time to learn a bit about
> SQL, and more so about the relational model, years before Django  
> came on
> the scene.
>
> Fourth layer: if you hold my feet to the fire to Do It All In Django,
> No SQL Please, no problem.  Just fetch all the rows, sorted by id, and
> iterate over them tossing off subtotals when the id column changes,
> viz., reinvent what the simple SQL statement would be doing with much
> greater data transfer requirements and reduced efficiency. (it was at
> this point that the urge to override the random .sig quite became
> irresistable)
>
> There ought to be quite a bit of onion left at his point, but I'm not
> sure what those layers would be.  Maybe implement the subtotal summing
> in postscript and produce the report by sending the sorted data to the
> print queue?  Hope it doesn't catch on fire...
>
> --
> This is like making a car shorter by cutting off a few inches
> from each end with a Sawzall.  Of course there's little benefit,
> because that's a dumb way to do it.  -- Neil R. Ormos
>
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