Bad error messages with singleRow

[agrafix]

If a query does not return anything (i.E. a plain INSERT), and I use the D.singleRow decoder, I get the following error:

SessionError (ResultError (UnexpectedResult "Unexpected result status: CommandOk"))

That's not helpful :-( Is there any way to improve this? I think we would only need to change

checkExecStatus :: (LibPQ.ExecStatus -> Bool) -> Result ()

so that one can provide a custom error message there and use that in the single function?

[nikita-volkov]

What kind of error message would you expect in such case?

[agrafix]

Something along the lines: Expected one row, but got an empty result?

[dispanser]

Just hit the same issue, but luckily a web search brought me here. Couldn't wrap my head around the fact that CommandOk could be a bad thing :)

[nikita-volkov]

PR welcome :)

[gfarrell]

Also hit the same issue, but using hasql-th -- I had a vectorStatement for a query which had no result, but thought hasql-th would have caught that there is no output of the query. Also didn't understand what was going wrong until I arrived at this issue.

I don't really feel confident that I'd be able to contribute to hasql as a bit of a baby Haskeller, but with some pointers I could try.

[mitchellwrosen]

@gfarrell Would you like to pair over a discord call or something? I'm also interested in improving this error message

[gfarrell]

@mitchellwrosen for a few reasons I'm probably abandoning Hasql in favour of Persistent so I probably won't be working on this, sorry!

[mitchellwrosen]

Hehe, no worries! (But also, you should use hasql ;))