QSqlQuery and QLineEdit

[GuL]

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


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

[spirit]

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


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


read for detailes QSqlQuery::next

[GuL]

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]

if you need only one result, then


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

[wysota]

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]

New code and still no result:


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);
}

[spirit]

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@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]

did you have compiled plugin or qt with mysql driver?

[GuL]

It is working.


#
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.

[GuL]

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

Renan

[spirit]

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

[GuL]

ok, but

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

what about Signals and Slots?


Renan

[spirit]

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?




what about Signals and Slots?


what slots and signals?

[GuL]

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,

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

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

Renan

[spirit]

for what purpose do you need this connection?

[GuL]

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]

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

[wysota]

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

[GuL]

here is spirit 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:

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:

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

Then I saw where is the error:


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

[GuL]

The result:

DISCO1

Any ideas?

Renan

[spirit]

ok. so, when you call your slot console hasn't any messages, right?

[spirit]

here is small example


#include <QApplication>
#include <QtGui>
#include <QtSql>

int main(int argc, char ** argv)
{
QApplication app(argc, argv);

QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName("test.db");

if (!db.open()) {
qDebug() << db.lastError().text();
return 0;
}

QSqlQuery query;
qDebug() << query.exec("CREATE TABLE test (id int PRIMARY KEY, test nvarchar)");

qDebug() << query.exec("INSERT INTO test VALUES(0, 'a')");
qDebug() << query.exec("INSERT INTO test VALUES(1, 'b')");
qDebug() << query.exec("INSERT INTO test VALUES(2, 'c')");
qDebug() << query.exec("INSERT INTO test VALUES(3, 'd')");
qDebug() << query.exec("SELECT test FROM test WHERE id = 1");
if (!query.next()) {
qDebug() << query.lastError().text();
return 0;
}
QLineEdit le(query.value(0).toString());
le.show();

return app.exec();
}

[wysota]

its code didn't compile, than I changed to:
If the code didn't compile, how come you managed to run an non-existing program? "Driver not loaded" is a runtime error, not compiler message.

[GuL]

Copying spirit code to my project didn't compile. here is spirit original 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);
}


In line 9, when we test if the database was successfully open,

query.lastError().text();
I got this error:

.\testemysql2.cpp(50) : error C2065: 'query' : undeclared identifier
.\testemysql2.cpp(50) : error C2228: left of '.lastError' must have class/struct/union
type is ''unknown-type''

when I canged line 9 to:

db.lastError().text();
I managed to run the program.

About the run-time error: "Driver not loaded"
It happened when I cut line 12 and paste it between line 2 and 3 and line 9 still was query.lastError().text();

I will try your code from the last post, spirit.
I had just install sqlite.

Renan



Renan

[GuL]

it shows me the letter "b" in a QLineEdit. Nice.

I will try to modify my code to work with mysql using your example.

Renan