QSqlQuery and QLineEdit

**GuL** · 14th August 2008, 17:14

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

Qt Code:

Switch view

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);
	}

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);
	}

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What I am doing wrong?

Renan

**spirit** · 14th August 2008, 17:29

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

Qt Code:

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

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

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read for detailes QSqlQuery::next

**GuL** · 14th August 2008, 17:34

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

**spirit** · 14th August 2008, 17:39

if you need only one result, then

Qt Code:

Switch view

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

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

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**wysota** · 14th August 2008, 17:39

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.

**GuL** · 14th August 2008, 17:52

New code and still no result:

Qt Code:

Switch view

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);
}

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);
}

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**spirit** · 14th August 2008, 17:57

Qt Code:

Switch view

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);
}

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);
}

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run this code and show console messages.

**GuL** · 14th August 2008, 18:18

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

**spirit** · 14th August 2008, 18:27

did you have compiled plugin or qt with mysql driver?

**GuL** · 14th August 2008, 18:40

It is working.

Qt Code:

Switch view

#
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;
....
     }

#
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;
....
     }

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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.

**GuL** · 14th August 2008, 19:05

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

Renan

**spirit** · 14th August 2008, 19:12

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

**GuL** · 14th August 2008, 19:24

ok, but

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

what about Signals and Slots?

Renan

**spirit** · 14th August 2008, 19:28

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?

Originally Posted by GuL

what about Signals and Slots?

what slots and signals?

**GuL** · 14th August 2008, 19:36

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:
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,

Qt Code:

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

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

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

Renan

**spirit** · 14th August 2008, 19:39

for what purpose do you need this connection?

**GuL** · 14th August 2008, 19:51

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

**spirit** · 14th August 2008, 19:53

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

**wysota** · 14th August 2008, 19:58

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

**GuL** · 14th August 2008, 20:10

here is spirit code:

Qt Code:

Switch view

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);
}

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);
}

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

Qt Code:

Switch view

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);
}

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);
}

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and then I got this error:

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

Then I saw where is the error:

Qt Code:

Switch view

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);

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);

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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

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