How to get data from intersystems cache db through ODBC? - c++

Question

This is how i try to get a data from db:
#include <QCoreApplication>
#include <QtCore>
#include <QtSql>
#include "iostream"
int main(int argc, char *argv[])
{
QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
db.setDatabaseName("DRIVER={InterSystems ODBC};SERVER=localhost;PORT=1972;DATABASE=USER;UID=_system;PWD=SYS; Unicode SQLTypes=1;");
if (!db.open())
{
std::cout << "Error opening database" << std::endl;
return -1;
}
else
{
QSqlQuery query;
if(query.exec("SELECT * FROM ACCOUNTS")){
std::cout << "Select succses!" << std::endl;
}
while (query.next())
{
std::cout << "Getting results..." << std::endl;
std::cout << query.value(0).toString().toStdString() << std::endl;
}
std::cout << "EXIT!" << std::endl;
return 0;
}
}
And after query.exec(...) query.next() is always false but I really know that there is a data in the table. This behavior reproduce in the case when I try to get data from sample tables of Cache DB. What did i do wrong?
Thanks for your help.

Answer 1

The problem was that connection config is wrong:
QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
db.setDatabaseName("DRIVER={InterSystems ODBC};SERVER=localhost;PORT=1972;DATABASE=USER;UID=_system;PWD=SYS; Unicode SQLTypes=1;");
it should be:
QSqlDatabase db = QSqlDatabase::addDatabase("QODBC3");
db.setDatabaseName("DRIVER={InterSystems ODBC35};SERVER=localhost;PORT=1972;DATABASE=USER;UID=_system;PWD=SYS; Unicode SQLTypes=1;");

Answer 2

[as I said in the comments, I'm not familiar with this API Just looking through the documentation as I answer]
the documentation for the constructor of QSqlQuery
Constructs a QSqlQuery object using the SQL query and the database db.
If db is not specified, or is invalid, the application's default
database is used. If query is not an empty string, it will be
executed.
This means your query is opened on the default database (whatever that means).
Looking at the QSqlDatabase documentation:
QSqlDatabase also supports the concept of a default connection, which
is the unnamed connection. To create the default connection, don't
pass the connection name argument when you call addDatabase().
however, you're giving a name argument in your addDatabase():
QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
... that means it is not the default connection.
My guess is that you should either:
QSqlDatabase db = QSqlDatabase::addDatabase();
or
QSqlQuery query=QSqlQuery(db);