Am 25.10.22 um 05:24 schrieb Tony Rietwyk:
Hi Oliver,
Can't answer your broader question, but I suspect the reason you are
seeing "No query Unable to fetch row" - error code: "" is because you
are not checking for an error after the prepare.
Oh my! I wasn't even aware that a call to QSqlQuery::prepare would
already validate the given query! And just for my own embarassment I
also noticed that I am even ignoring the boolean return value of that
method. And while I do compile my application with various compilers on
Windows, macOS and Linux and have various "Clang-Tidy and Clazy" and
some other "modern/core C++" checks enabled, none is complaining so far
about this "ignored return statement" so far (will go and see whether
other checks - if enabled - will warn about this. I am pretty sure that
there must be /some/ code validator test that checks for ignored return
values).
(In my little defense: I am not executing any user-provided SQL. All SQL
in my application is hand-crafted and "hardcoded" SQL, and any failure
would indicate a "programming error" anyway, that hopefully would be
detected during manual testing - I am talking about a "one man open
source app", so this is acceptable for my given situation ;))
For the record, this is also (of course, as usually in an excellent
manner) documented here, so for the record:
https://doc.qt.io/qt-6/qsqlquery.html#prepare
Even noting that "Some databases choose to delay preparing a query until
it is executed the first time. In this case, preparing a syntactically
wrong query succeeds, but every consecutive exec
<https://doc.qt.io/qt-6/qsqlquery.html#exec-1>() will fail."
The fact that the "prepare" already validates the SQL is actually good
news, because it could help me to "test at runtime" whether the given
SQLite plugin would support sin(), cos() etc., and if not I could fall
back to some simpler "distance formula".
So thank you so much to making me aware that I should - at least - also
check the result of the prepare() statement (even if it is "hardcoded
and tested SQL"). ;)
Cheers, Oliver
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