Re: Some questions about file handling + some other things

On Wed, Mar 24, 2021 at 09:31:42AM -0400, John P. Rouillard wrote:
> >Looks good (without having tested anything) but I'm not sure to_raw is
> >the correct method to use here in sorting.
> 
> I don't understand. sort_repr is the method I am using. to_raw is
> just a (poorly??) chosen variable name.

Ah. The hyperdb has "from_raw" methods, I thought there would be a
"to_raw", too and that you did reuse that.

> >It is also worth a regression test: If sorting of numbers and/or dates
> >works in SQL (for everything but Multilink properties) I'm quite sure
> >that it would break for anydbm which always sorts in python.
> 
> Yes, Probably needs more data in the db to actually test the ordering
> across multiple items. Anydbm I'll bet is currently broken since it
> would use a string sort order not an integer/number sort order in its
> sorting calls.

No, the regression-test tests that.
But it may be that sorting values that can contain NULL values will not
work.

> >From an implementation point of view, sorting null last requires a
> value to replace null/None so sort(key=...) doesn't throw an error
> trying to sort None against any other type. Without knowing something
> about the property's possible values I don't see how the code can
> choose a suitable value.

I'm doing this explicitly for Postgres (and probably other backends),
the generated SQL for filter calls looks like this:

...
order by (lower(_someclass._title) is not NULL),lower(_someclass._title)
...

So its perfectly fine to put NULL values first or last. And it doesn't
need many changes to make it work.

> Consider a multilink called surveys with a 'rating' property. We want
> to display the links in rating order. 'rating' has values [-5,5] where
> 0 is neutral. You want "no rating given"/unset to sort as 0. I am sure
> there are other examples. Note if 'rating' had values [0,10] then 'no
> rating' should be 5. If you wanted all 'no value given' to sort at the
> end, you choose 11 as the 'no rating given" value.

Hmm, in that case I would not allow NULL values. Should be set to 0 by
an auditor.

> Thoughts?

I'm reluctant to add an explicit property where you can sort NULL values
into the middle of everything else. Doesn't feel right :-)

Note that so far I was considering sorting by hyperdb.filter (and html
wrapper classes) and you were considering only the multilink sorting as
far as I understand.

Ralf
-- 
Dr. Ralf Schlatterbeck                  Tel:   +43/2243/26465-16
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