query() for prepared statements

[jtv]

This is a re-filing of an older ticket that got hijacked for a different problem: #644.

The original question from @maresc-g was:

《We're looking to upgrade our version of pqxx in our application so I just came across the release note of the 7.7.4 in which you ask for feedback on if we still use pqxx::result.
I'd like to use the feature to automatically convert types like with query() but we only use prepared queries so we call exec_prepared() which still returns a pqxx::result.
Is it planned to add this for prepared queries as well in future releases ?》

[jtv]

In PR #875 I bring this a step closer.

[jtv]

I'm redoing the "exec" functions, so that parameterised statements, regular statements, and prepared statements will look much more alike. Next I want to refactor the exec1(), exec_n(), prepared_exec1(), etc. by moving the row-count checks out of those functions. Instead, you'll make a separate function call to check that you're getting the number of rows you expect.

That will greatly reduce, in the end, the number of exec functions that I need to support. As a part of the ongoing work I think I can implement query() for both prepared statements and parameterised statements, without too much trouble. This work is happening in #875.

[alexolog]

That sounds like a big breaking change. Not something people will be looking for.

[jtv]

The existing functions will stay around for a long time, as always, with a deprecation attribute so everybody gets warnings when they compile code that uses them, telling them what to use instead. This is standard procedure.

[jtv]

Actually, this is resolved now. You can now call query() and pass a prepped statement instead of an SQL string.