QSqlQuery and QLineEdit

Why this code doesn't work?
I want to show the result of this query in the QLineEdit.

Code:

---

void testeMYSQL2::on_pushButton_clicked()
{
	QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
        db.setHostName("localhost");
        db.setDatabaseName("teste");
        db.setUserName("root");
        db.setPassword("");
	db.open();
/*	if (!db.open()){
		QMessageBox::critical(0, tr("Error"), 
		QString("The error:\n%1").arg(db.lastError().text())); 
	 }
	 else{
		QMessageBox::information(0, tr("OK"), QString("The is NO error\n"));
	 }
*/
	 QSqlQuery query;
	 query.exec("select nome_prod from produtos where cod_prod = 1");
	query.next();
	for (int i = 0; i < record.count(); i++) {
		QString name = query.value(i).toString();
		nameEdit->setText(name);
	}

---

What I am doing wrong?

Renan

at first, you have only one column (according to your query text)
second, you set position only on first record (query.next())
and then try to read data from non-existed columns (you have only one column!)
so, try this code

Code:

---

....
     while (query.next()) {
         QString data = query.value(0).toString();//first column == nome_prod
         ....
     }
     ....

---

read for detailes QSqlQuery::next

The result of this query is only one line and one column...

The result is DISCO1

I just want to see this word in the QLineEdit, thats why I didn't use the while loop.
Why the result doesn't show? What signal/slot should I use?
Signal->clicked()
Slot-> ???

Renan

if you need only one result, then

Code:

---

query.next();
QString res = query.valut(0).toString();

---

I don't know what "record" is in your case, but I'd guess it's an invalid QSqlRecord with a count of 0, thus your loop never gets executed. I'd suggest doing it the way spirit said.

New code and still no result:

Code:

---

void testeMYSQL2::on_pushButton_clicked()
{
	QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
        db.setHostName("localhost");
        db.setDatabaseName("teste");
        db.setUserName("root");
        db.setPassword("teste1234");
	db.open();
/*	if (!db.open()){
		QMessageBox::critical(0, tr("Error"), 
		QString("The error:\n%1").arg(db.lastError().text())); 
	 }
	 else{
		QMessageBox::information(0, tr("OK"), QString("The is NO error\n"));
	 }
*/
	 QSqlQuery query;
	 query.exec("select nome_prod from produtos where cod_prod = 1");
 
	query.next();
		QString name = query.value(0).toString();
		nameEdit->setText(name);
}

---

Code:

---

void testeMYSQL2::on_pushButton_clicked()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
        db.setHostName("localhost");
        db.setDatabaseName("teste");
        db.setUserName("root");
        db.setPassword("teste1234");
    if (!db.open()) {
          qDebug() << query.lastError().text();
          return;
    }
 
     QSqlQuery query;
     if (!query.exec("select nome_prod from produtos where cod_prod = 1")) {
          qDebug() << query.lastError().text();
          return;
     }
 
        if (!query.next()) {
          qDebug() << query.lastError().text();
          return;
        }
        QString name = query.value(0).toString();
        nameEdit->setText(name);
}

---

run this code and show console messages.

gul@gul-laptop:~/qt/testemysql2$ ./testemysql2
QSqlQuery::exec: database not open
"Driver not loaded Driver not loaded"

=-=-=-=-=-=-==-=-=-=-

It doesn't show any messages:

gul@gul-laptop:~/qt/testemysql2$ ./testemysql2

did you have compiled plugin or qt with mysql driver?

It is working.

Code:

---

#
void testeMYSQL2::on_pushButton_clicked()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
        db.setHostName("localhost");
        db.setDatabaseName("teste");
        db.setUserName("root");
        db.setPassword("teste1234");
    if (!db.open()) {
          qDebug() << query.lastError().text();
          return;
    }
 
     QSqlQuery query;
     if (!query.exec("select nome_prod from produtos where cod_prod = 1")) {
          qDebug() << query.lastError().text();
          return;
....
     }

---

this line, the fisrt one: qDebug() << query.lastError().text();

should be: qDebug() << db.lastError().text();

to compile.
because it is testing its connection

never mind., but it doesn't show anything to me.

what can I do to get those lastError() ???

Renan

does qDebug() << db.lastError().text(); return nothing?
if QSqlDatabase::lastError doesn't return anything then everything is ok.

ok, but

if everything is ok, why QLineEdit doesn't show the result?

what about Signals and Slots?


Renan

Quote:

---

Originally Posted by GuL

ok, but
if everything is ok, why QLineEdit doesn't show the result?

---

you showed error message on console "driver not loaded". doesn't this error appear anymore?

Quote:

---

Originally Posted by GuL

what about Signals and Slots?

---

what slots and signals?

Quote:

---

Quote:
Originally Posted by GuL View Post
ok, but
if everything is ok, why QLineEdit doesn't show the result?
you showed error message on console "driver not loaded". doesn't this error appear anymore?

---

No, it doesnt. I have changed your code in order to compile and that error happened. Than I changed it again and it worked!

Quote:

---

Quote:
Originally Posted by GuL View Post
what about Signals and Slots?
what slots and signals?

---

Should I connect pushbutton to qlineedit?
if your answer is yes,

Code:

---

QObject::connect(pushButton, SIGNAL(clicked()), nameEdit, SLOT( ????????? ));

---

what should be the slot for nameEdit? I'm using the Designer to create the interface.

Renan

for what purpose do you need this connection?

I thought I would need it to make the result to show in the QLineEdit. -- Now I know it isn't necessary.

But my problem still persist, no result in QLineEdit.

Any ideas?

Renan

check the result of your query in sqlbrowser which is located in QTDIR/demos/sqlbrowser.

Could you please say what exactly did you do to eliminate the "Driver not loaded" message?

here is spirit code:

Code:

---

void testeMYSQL2::on_pushButton_clicked()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
        db.setHostName("localhost");
        db.setDatabaseName("teste");
        db.setUserName("root");
        db.setPassword("teste1234");
    if (!db.open()) {
          qDebug() << query.lastError().text();
          return;
    }
 
     QSqlQuery query;
     if (!query.exec("select nome_prod from produtos where cod_prod = 1")) {
         qDebug() << query.lastError().text();
          return;
     }
 
        if (!query.next()) {
          qDebug() << query.lastError().text();
          return;
        }
        QString name = query.value(0).toString();
        nameEdit->setText(name);
}

---

its code didn't compile, than I changed to:

Code:

---

void testeMYSQL2::on_pushButton_clicked()
{
        QSqlQuery query; 
       QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
        db.setHostName("localhost");
        db.setDatabaseName("teste");
        db.setUserName("root");
        db.setPassword("teste1234");
    if (!db.open()) {
          qDebug() << db.lastError().text();
          return;
    }
 
         if (!query.exec("select nome_prod from produtos where cod_prod = 1")) {
         qDebug() << query.lastError().text();
          return;
     }
 
        if (!query.next()) {
          qDebug() << query.lastError().text();
          return;
        }
        QString name = query.value(0).toString();
        nameEdit->setText(name);
}

---

and then I got this error:

Quote:

---

gul@gul-laptop:~/qt/testemysql2$ ./testemysql2
QSqlQuery::exec: database not open
"Driver not loaded Driver not loaded"

---

Then I saw where is the error:

Code:

---

void testeMYSQL2::on_pushButton_clicked()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
        db.setHostName("localhost");
        db.setDatabaseName("teste");
        db.setUserName("root");
        db.setPassword("teste1234");
    if (!db.open()) {
          qDebug() << db.lastError().text();
          return;
    }
 
     QSqlQuery query;
     if (!query.exec("select nome_prod from produtos where cod_prod = 1")) {
         qDebug() << query.lastError().text();
          return;
     }
 
        if (!query.next()) {
          qDebug() << query.lastError().text();
          return;
        }
        QString name = query.value(0).toString();
        nameEdit->setText(name);

---

Then it worked, but still I don't see the result in the QLineEdit.

Now I will try what spirit said above. I will post the result in a few seconds.

Renan