Database not opening error qt c++ - c++

Question

I have created a class named MainWIndow which has a method(getconnOpen) to provide database connection! following is my code!
MainWindow.h
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
QSqlDatabase mydb;
bool getconnOpen(QString uname,QString pword,QString ip,int port,QString dbname){
mydb=QSqlDatabase::addDatabase("QOCI");
mydb.setUserName(uname);
mydb.setPassword(pword);
mydb.setHostName(ip);
mydb.setPort(port);
mydb.setDatabaseName(dbname);
mydb.open
return true;
}
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
void on_pushButton_clicked();
private:
Ui::MainWindow *ui;
};
MainWindow.cpp
void MainWindow::on_pushButton_clicked()
{
Dialog *dialog1=new Dialog(this);
if(getconnOpen(ui->lineEdit->text(),ui->lineEdit_2->text(),ui->lineEdit_3->text(),ui->lineEdit_4->text().toInt(),ui->lineEdit_5->text()){
dialog1->show();
}
}
Dialog.h
class Dialog : public QDialog
{
Q_OBJECT
public:QSqlDatabase mydb;
public:
explicit Dialog(QWidget *parent = 0);
~Dialog();
private slots:
void on_pushButton_clicked();
Dialog.cpp
void Dialog::on_pushButton_clicked()
{
QSqlQueryModel modal = new QSqlQueryModel();
QSqlQuery qry=new QSqlQuery(mydb);
qry->prepare("select User FROM USERS");
qry->exec();
modal->setQuery(*qry);
ui->tableView->setModel(modal);
}
Though I opened the connection in MainWindow.h the query in dialog.cpp gives an error stating "database not open" ! But I opened the databse in MainWindow.cpp! How can I correct this?

Answer 1

Try something like this (mind you I do not have time to test this so you may need to tweak it) And I am annoyed that it created a cyclical dependence between the MainWindow and Dialog.. you can undo that by creating a dbmanager class or using a shared pointer to the mydb instead. but this is the quickest thing I could type for you without having to redesign all your code.
MainWindow.h
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
QSqlDatabase mydb;
bool getconnOpen(QString uname,QString pword,QString ip,int port,QString dbname){
mydb=QSqlDatabase::addDatabase("QOCI");
mydb.setUserName(uname);
mydb.setPassword(pword);
mydb.setHostName(ip);
mydb.setPort(port);
mydb.setDatabaseName(dbname);
// Return the actual state of the db instead of return true.
return mydb.open();
}
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
void on_pushButton_clicked();
private:
Ui::MainWindow *ui;
};
MainWindow.cpp
void MainWindow::on_pushButton_clicked()
{
Dialog *dialog1=new Dialog(this);
if(getconnOpen(ui->lineEdit->text(),ui->lineEdit_2->text(),ui->lineEdit_3->text(),ui->lineEdit_4->text().toInt(),ui->lineEdit_5->text()){
dialog1->show();
}
}
Dialog.h
class Dialog : public QDialog
{
Q_OBJECT
public:
explicit Dialog(QWidget *parent = 0);
~Dialog();
private slots:
void on_pushButton_clicked();
Dialog.cpp
void Dialog::on_pushButton_clicked()
{
QSqlQueryModel modal = new QSqlQueryModel();
// get the db object from the parent widget, if the parent widget returned is not of the MainWindow type then dynamic_cast will return NULL.
MainWindow *mainWindow = dynamic_cast<MainWindow(parentWidget());
// if all went well then mainWindow is not NULL but should test first.
if (mydb != NULL)
{
QSqlQuery qry=new QSqlQuery(mainWindow->mydb);
qry->prepare("select User FROM USERS");
qry->exec();
modal->setQuery(*qry);
ui->tableView->setModel(modal);
}
// do something else if the pointer is NULL.
}
I am not happy with doing it this way:
*********** OK FOUND THE RIGHT WAY TO DO IT I THINK!*********************
from this post Handling QSqlDatabase connections
looks like QSqlDatabase is already a connection manager so you add the connection once and retrieve it by name from your other form. Again I do not have the ability to test this but this would be a better approach as it uses the QT connection manager as it is intended and there are no cyclical dependencies between MainWindow and the Dialog.
MainWindow.h
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
QSqlDatabase mydb;
bool getconnOpen(QString uname,QString pword,QString ip,int port,QString dbname){
// Add the database by name so you can retrieve it later. I would also
// not hardcode the name like this but this.. yuck but hey you can fix
// that yourself ;)
mydb=QSqlDatabase::addDatabase("QOCI", "MyDbConnection");
mydb.setUserName(uname);
mydb.setPassword(pword);
mydb.setHostName(ip);
mydb.setPort(port);
mydb.setDatabaseName(dbname);
// Return the actual state of the db instead of return true.
return mydb.open();
}
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
void on_pushButton_clicked();
private:
Ui::MainWindow *ui;
};
MainWindow.cpp
void MainWindow::on_pushButton_clicked()
{
Dialog *dialog1=new Dialog(this);
if(getconnOpen(ui->lineEdit->text(),ui->lineEdit_2->text(),ui->lineEdit_3->text(),ui->lineEdit_4->text().toInt(),ui->lineEdit_5->text()){
dialog1->show();
}
}
Dialog.h
class Dialog : public QDialog
{
Q_OBJECT
public:
explicit Dialog(QWidget *parent = 0);
~Dialog();
private slots:
void on_pushButton_clicked();
Dialog.cpp
void Dialog::on_pushButton_clicked()
{
QSqlQueryModel modal = new QSqlQueryModel();
// make sure the database exists.
if (QSqlDatabase::contains("MyDbConnection");)
{
// retrieve the database by name from the database manager.
QSqlQuery qry=new QSqlQuery(QSqlDatabase::database("MyDbConnection"));
qry->prepare("select User FROM USERS");
qry->exec();
modal->setQuery(*qry);
ui->tableView->setModel(modal);
}
// do something else if the pointer is NULL.
}