Selecting data from mysql using qt?

doforumda

i am trying to select data from mysql db using qt. here is my code
@
#include <QApplication>
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>
#include <QDebug>
//#include <QString>
//#include "../connection.h"
#include "db.h"

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

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
db.setDatabaseName("testTwo");
db.setUserName("root");
db.setPassword("");
db.setHostName("localhost");

//bool ok = db.open();

QSqlQuery query;
query.exec&#40;"SELECT * FROM testTable"&#41;;
while(query.next(&#41;&#41; {
    QString firstName = query.value(0&#41;.toString();
    QString secondName = query.value(1).toString();
    qDebug() << firstName << secondName;
}
return a.exec(&#41;;

}
@

this piece of code displays this error
@
invalid use of incomplete type ‘struct QVariant’ main.cpp 25
forward declaration of ‘struct QVariant’ qobject.h 66
invalid use of incomplete type ‘struct QVariant’ main.cpp 26
forward declaration of ‘struct QVariant’ qobject.h 66
@
please help how can i solve this problem?

? Offline

Line no. 22 and 23, can just be replaced with ...

@
QSqlQuery query("SELECT * FROM testTable");
@

But also, do check the documentation for QSqlQuery, where it is recomended NOT to use SELECT *

doforumda

now i changed it to this
@
query.exec("SELECT firstname,lastname FROM testTable");
@
still the same errors

and i am following this link "Your text to link here...":http://doc.trolltech.com/4.7/sql-sqlstatements.html

tony

Maybe an "#include <QVariant>" is missing at the top?

T.

MTK358

Why not just

@#include <QtCore>
#include <QtSql>@

and not worry about every single class you use?

tony

That can be a solution only when you're testing something. So, in this case, I agree with you, let's avoid such worries.

But if your project grows up, it's better to include what's needed, otherwise your compilation time can increase a lot.

T.

doforumda

i add #include <QVariant>

now it is saying
@
QSqlQuery::exec: database not open
@

Dmytro

Try to use QSqlQuery::lastError() for find problem

doforumda

what is the problem now in my code why it is not opening database?

tony

Did you leave

@
//bool ok = db.open();
@

commented?

doforumda

well i changed my code to this and added lastError as well

@
#include <QApplication>
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>
#include <QDebug>
#include <QString>
#include <QVariant>
//#include <QtCore>
//#include <QtSql>
//#include "../connection.h"
#include "db.h"

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

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
db.setDatabaseName("testTwo");
db.setUserName("root");
db.setPassword("");
db.setHostName("localhost");

//bool ok = db.open();

QSqlQuery query;
query.exec&#40;"SELECT firstname,lastname FROM testTable"&#41;;
while(query.next()) {
    QString firstName = query.value(0).toString();
    QString secondName = query.value(1).toString();
    qDebug() << "First Name: " << firstName << "Last Name:" << secondName;
    qDebug() << db.lastError();
}
return a.exec&#40;&#41;;

}
@

it still says QSqlQuery::exec: database not open

doforumda

it is still as commented
[quote author="Antonio Di Monaco" date="1286818410"]Did you leave

@
//bool ok = db.open();
@

commented?[/quote]

Dmytro

Try uncomment line 23

doforumda

i uncomment line 23 and comment everything below line 23 then it just says
@
Starting /home/zafar/c++/dbExample-build-desktop/dbExample...
@

and stucks there

Dmytro

OH! You use SQL code before
a.exec()
!
Are you sure?

Create standart QT GUI application and wrote sql code in mainwindow module.

doforumda

i am new to qt. how can i create Qt Gui App and do you mean i should write sql code in mainwindow.h file?

doforumda

right now i have three files. db.h, db,cpp and main.cpp

Dmytro

Run QT Creator.
Use menu File/new file or project.
Select QT Gui application.
...
and select SQL checkbox
...
and write sql code in MainWindow.cpp
...
and see SQL Example please

doforumda

well i tried "File/new file or project and select qt gui app" but i ddint find any sql checkbox anywhere in creating new project

Dmytro

no coments...
How can I send you screenshot?