Improve error message for empty argument to :csv ?

[njlr]

I have a query like this:

const fetchBooks = (db, titles) => db.query(`SELECT id
    FROM books 
    WHERE title IN ( $<titles:csv> ) `, {
      titles,
    });

When titles is [], the error message is quite confusing:

... error: syntax error at or near ")" ...

This is the error forwarded from the underlying pg library, but perhaps pg-promise could provide a better error for this scenario?

Something like...

Empty arrays are not valid for the ":csv" syntax.

(Related: brianc/node-postgres#1079)

[vitaly-t]

This is the error forwarded from the underlying pg library, but perhaps pg-promise could provide a better error for this scenario?

It can't, because filter :csv is generic, and it doesn't know in which context you are using it.

You should instead check titles.length, and when it is 0, do not execute such invalid query at all, i.e. having IN () is invalid in queries, and that's what you are trying to execute, hence the error.

[njlr]

Yes, that was my work-around. It would have been easier to identify the error with a more specific message though.

If there are cases in which :csv is valid without any elements then my suggestion will not work.

[vitaly-t]

If there are cases in which :csv is valid without any elements then my suggestion will not work.

There are plenty, as the filter is generic, it is used in many places, not just for IN () statements.

[vitaly-t]

Related issue on StackOverflow: https://stackoverflow.com/questions/48344888/best-practice-for-creating-sql-select-queries-while-handling-potential-undefined

[vitaly-t]

More on this question: WHERE col IN Query with empty array as parameter