Invalid QSqlRecord after performing another query to DB

[crew4ok]

Hi everyone!

I have some problems with using QtSql.
So here's the code first:


QSqlQuery q1(db_connection), q2(db_connection);
q1.exec("SELECT * from users");
while(q1.next())
{
q2.exec("delete from table1");
if (!q2.isValid())
qDebug() << "q2 is not valid";

if (q1.isActive() && q1.isValid())
qDebug() << q1.record();
}


So there are two queries to one database: q1 is absolutely correct and should return several result rows, but q1 is some wrong query.
The question is why QSqlQuery::record() of q1 returns empty data after executing query q2?

I'm using MySQL 5.5.
I repeated this behaviour on qt 4.7.1 and qt 4.8.1 in Windows and Linux.

P.S.: Sorry for my english.

[crew4ok]

Any suggestions? :/

[ChrisW67]

Works fine here with Sqlite but not MySql... it is going to be a MySQL quirk.

Here is my take:


#include <QtCore>
#include <QtSql>
#include <QDebug>


int main(int argc, char *argv[])
{
QCoreApplication app(argc, argv);

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
db.setDatabaseName("testdb");
db.setUserName("user");
db.setPassword("password");
if (db.open()) {
// Create a test table
db.exec("CREATE TABLE zzz_test (a int, b varchar(10))");
db.exec("INSERT INTO zzz_test VALUES (1, 'Apple')");
db.exec("INSERT INTO zzz_test VALUES (2, 'Banana')");
db.exec("INSERT INTO zzz_test VALUES (3, 'Cherry')");

QSqlQuery q1(db);
QSqlQuery q2(db); // Fails badly if declared here
if (q1.exec("SELECT * from zzz_test")) {
while(q1.next()) {
// QSqlQuery q2(db); // fails less badly here because it is destroyed at the end of the loop
qDebug() << "Before q2" << q1.record() << q1.lastError().text();

// Any failing query
if (!q2.exec("select * from zzz_nonexistent"))
qDebug() << "q2 failed" << q2.lastError().text();
// q2.clear(); // Adding this fixes the next line

qDebug() << "After q2" << q1.record() << q1.lastError().text();
}
}

db.exec("DROP TABLE zzz_test");
}

return 0;
}


I'd be inclined to raise a bug.