On 12/05/2014 02:30 AM, Matt Newell wrote:
The explanation of PQgetFirstQuery makes it sound pretty hard to match
up the result with the query. You have to pay attention to PQisBusy.
PQgetFirstQuery should also be valid after
calling PQgetResult and then you don't have to worry about PQisBusy, so I
should probably change the documentation to indicate that is the preferred
usage, or maybe make that the only guaranteed usage, and say the results
are undefined if you call it before calling PQgetResult. That usage also
makes it consistent with PQgetLastQuery being called immediately after
PQsendQuery.
I changed my second example to call PQgetFirstQuery after PQgetResult instead
of before, and that removes the need to call PQconsumeInput and PQisBusy when
you don't mind blocking. It makes the example super simple:
PQsendQuery(conn, "INSERT INTO test(id) VALUES (DEFAULT),(DEFAULT)
RETURNING id");
query1 = PQgetLastQuery(conn);
/* Duplicate primary key error */
PQsendQuery(conn, "UPDATE test SET id=2 WHERE id=1");
query2 = PQgetLastQuery(conn);
PQsendQuery(conn, "SELECT * FROM test");
query3 = PQgetLastQuery(conn);
while( (result = PQgetResult(conn)) != NULL )
{
curQuery = PQgetFirstQuery(conn);
if (curQuery == query1)
checkResult(conn,result,curQuery,PGRES_TUPLES_OK);
if (curQuery == query2)
checkResult(conn,result,curQuery,PGRES_FATAL_ERROR);
if (curQuery == query3)
checkResult(conn,result,curQuery,PGRES_TUPLES_OK);
}
Note that the curQuery == queryX check will work no matter how many results a
query produces.
Oh, that's what the PQgetLastQuery/PQgetNextQuery functions work! I
didn't understand that before. I'd suggest renaming them to something
like PQgetSentQuery() and PQgetResultQuery(). The first/last/next names
made me think that they're used to iterate a list of queries, but in
fact they're supposed to be used at very different stages.
- Heikki
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