Hello Matt,
it may be a bit of an oversight that no such procedure exists in the
SQLite3 egg, but you could define something like this:
(define (one-result/default default db sql . parameters)
(call-with-temporary-statements
(lambda (stmt)
(apply bind-parameters! stmt parameters)
(if (step! stmt)
(column-data stmt 0)
default))
db sql))
[untested, and leaving the usual "overloads" for statement objects vs. SQL
source as an exercise to the reader 😉]
Ciao,
Thomas
Am Mi., 8. Juni 2022 um 20:10 Uhr schrieb Matt Welland <[email protected]>:
> The problem: retrieve one value from a query, if there is no matching
> row return a default.
>
> Method 1: use for-each-row, overwrite the default with found values
> Method 2: use first-result, on exception return the default
> Method 3: use fold-row (wasn't an option when I first wrote the code)
>
> My question is, which of these is the "right" way to do what I want? Is
> there another, better, way? Note that method #2 has problems in my
> program but it might be due to my using chicken 4.10 (for now).
>
> ==additional details==
>
> Method 1, for-each-row, was my original approach and seemed to work
> fine.
>
> Then, in the midst of a major rewrite I tried to use first-result. It
> seemed odd to me to use an exception this way but I assumed (wrongly?)
> it was a fancy software engineery way to do things since the sqlite3
> egg did not provide any direct way to do what I want.
>
> However I hit a strange scalability issue with database locks happening
> only a few hours into a run. After a lot of fruitless debug and on a
> hunch, I replaced the first-result with a for-each-row and now am able
> to run ten of thousands of tests over many hours (still not perfect,
> work progresses).
>
> I plan to replace use of for-each-row with something like:
>
> (define (get-id db name default)
> (fold-row (lambda (row)
> (car row))
> #f
> db "SELECT id FROM tests WHERE testname=?" name))
>
> Thanks.
>
>
>
