Re: DatabaseMetaData and Transactions

Tom Lane wrote:
> Oliver Jowett <oliver(at)opencloud(dot)com> writes:
>
>>You're going to have to pass metadata down, or change your queries to
>>explicitly cast the parameters in the SQL itself. The driver has exactly
>>the same problem as your code does -- with the v3 protocol it needs to
>>provide a type for the parameter, but if it's just provided as a string
>>the only type it can assume is text..
>
>
> Is there any chance of a win in passing the type across to the backend
> as "unknown", and seeing if the backend can infer something reasonable?
> For example given
> WHERE int4col = ?
> it'd be reasonable to infer the type of the ? symbol as int4, and that
> logic has been built into the backend since forever.

It's a possibility, but:

a) really this is an application bug (admittedly a common one) .. the
JDBC API provides type info for parameters, and if the application
claims that a parameter is a String, why should the driver second-guess it?

b) there were some cases (? IS NULL and some cases with function args,
from memory?) which didn't work when an unknown OID was used, so to some
extent you're exchanging one problem for another.

We do pass the unknown OIDs for "untyped" (JDBC Types.OTHER) NULLs
already. Passing unknown for setObject(column, value, Types.OTHER) seems
reasonable given what we do with setNull().. but that doesn't solve the
problem of applications using setString() for parameters that actually
need to be some other type.

-O