Error executing query: "Driver not loaded" - Need Assistance

[eclispe]

Hello Qt community,

I hope this message finds you well. I'm currently facing an issue while executing a query, and I'm seeking guidance to resolve it. I appreciate your expertise and any assistance you can provide.

• Error Details:
  I'm currently facing an issue where I can insert data into my database successfully, but encountering difficulties when trying to read or retrieve data .
  I encountered the following error message: "Error executing query: Driver not loaded."

• Database Type: Oracle

• Database Connection Driver: QODBC

• Programming Language: c++

This is my connection function :

bool connexion::connect(){
bool test=false;
     QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
     db.setDatabaseName("ProjectDataBase");
     db.setUserName("eclipse");
     db.setPassword("eclipse");

     if (db.open())
     {
         test=true;
     }

 return  test ;
}

This is my insert and display funtions :

/*DISPLAY*/
QSqlQueryModel * client::display_all_clients(){
    QSqlQueryModel *model = new QSqlQueryModel;
    model->setQuery("SELECT * FROM CLIENTS");
    if (model->lastError().isValid()) {
        qDebug() << "Error executing query:" << model->lastError().text();
    }
    model->setHeaderData(0, Qt::Horizontal, QObject::tr("IDENTIFIANT"));
    model->setHeaderData(1, Qt::Horizontal, QObject::tr("FIRST NAME"));
    model->setHeaderData(2, Qt::Horizontal, QObject::tr("NAME"));
    model->setHeaderData(3, Qt::Horizontal, QObject::tr("DATE OF BIRTH"));
    return model ;
}
/*ADD*/
bool client::add_client() {
    QSqlQuery query;
    query.prepare("INSERT INTO CLIENTS (CIN, FIRSTNAME, NAME, DOB) "
                  "VALUES (?, ?, ?, ?)");
    query.bindValue(0, cin);
    query.bindValue(1, firstName);
    query.bindValue(2, name);
    query.bindValue(3, dob);
    return query.exec();
}

Thank you in advance for your time and assistance.

[JonB]

@eclispe
The only was you should be able to get "Driver not loaded" is if you call your setQuery() without having previously done the addDatabase("QODBC") in the same session.

[SGaist]

Hi and welcome to devnet,

In addition to @JonB, you don't do anything if the database fails to open. You should at least print the error message.

[eclispe]

@JonB @SGaist I apologize for the lack of information in the post .
this is my main.cpp :

#include "mainwindow.h"
#include "connexion.h"
#include <QApplication>
#include <QMessageBox>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
       connexion c;
       bool test=c.connect();
       if(test)
       {w.show();
           QMessageBox::information(nullptr, QObject::tr("database is open"),
                       QObject::tr("connection successful.\n"
                                   "Click Cancel to exit."), QMessageBox::Cancel);

   }
       else
           QMessageBox::critical(nullptr, QObject::tr("database is not open"),
                       QObject::tr("connection failed.\n"
                                   "Click Cancel to exit."), QMessageBox::Cancel);

    return a.exec();
}

and this is the result :

[Christian Ehrlicher]

And from where do you call the select? From the mainwindow ctor?

[JonB]

@eclispe said in Error executing query: "Driver not loaded" - Need Assistance:

I'm currently facing an issue where I can insert data into my database successfully, but encountering difficulties when trying to read or retrieve data .

I do not believe this. I do not believe an INSERT works but a SELECT does not.

As @Christian-Ehrlicher says. Please provide an actual complete minimal example of your code, not snippets.

[eclispe]

All right @Christian-Ehrlicher @JonB , here is my complete code :

• headers :

connexion.h :

#ifndef CONNEXION_H
#define CONNEXION_H
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>
class connexion
{
public:
    connexion();
    bool connect();
};

#endif // CONNEXION_H

client .h :

#ifndef CLIENT_H
#define CLIENT_H
#include<QString>
#include<QSqlQuery>
#include<QSqlQueryModel>
#include<QDebug>
#include<QObject>
#include "connexion.h"
class client 
{
private :
   int cin  ;
   QString name ;
   QString firstName ;
   QString dob ;
public:
 /*constructor*/
client();
client(int , QString ,QString ,QString);
/* getters */
int getCin();
QString getName();
QString getFirstName();
QString getDateOfBirth();
/* setters */
void setCin(int cin);
void setName(QString name);
void setFirstName(QString firstName);
void setDateOfBirth(QString dob);
/* CRUD */
QSqlQueryModel * display_all_clients();
bool add_client();
bool delete_client(int cin);
bool update_client();
};

#endif // CLIENT_H

mainwindow.h :

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QStackedWidget>
#include <QPushButton>
#include <QTableWidget>
#include <QApplication>
#include <QMessageBox>
#include <iostream>
#include"client.h"
#include "connexion.h"
QT_BEGIN_NAMESPACE
namespace Ui {
class MainWindow;
}
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
private slots:
    void on_employees_clicked();

    void on_clients_clicked();

    void on_stock_clicked();

    void on_settings_clicked();

    void on_about_us_clicked();

    void on_home_clicked();

    void on_home_2_clicked();

    void on_employees_2_clicked();

    void on_clients_2_clicked();

    void on_stock_2_clicked();

    void on_settings_2_clicked();

    void on_about_us_2_clicked();

    void on_home_3_clicked();

    void on_employees_3_clicked();

    void on_clients_3_clicked();

    void on_stock_3_clicked();

    void on_settings_3_clicked();

    void on_about_us_3_clicked();
    void on_home_4_clicked();

    void on_employees_4_clicked();

    void on_clients_4_clicked();

    void on_stock_4_clicked();

    void on_settings_4_clicked();

    void on_about_us_4_clicked();
    void on_home_5_clicked();

    void on_employees_5_clicked();

    void on_clients_5_clicked();

    void on_stock_5_clicked();

    void on_settings_5_clicked();

    void on_about_us_5_clicked();
    void on_home_6_clicked();

    void on_employees_6_clicked();

    void on_clients_6_clicked();

    void on_stock_6_clicked();

    void on_settings_6_clicked();

    void on_about_us_6_clicked();

    void on_list_op_clicked();

    void on_add_op_clicked();

    void on_up_op_clicked();

    void on_del_op_clicked();

    void on_list_op_1_clicked();

    void on_add_op_1_clicked();

    void on_up_op_1_clicked();

    void on_del_op_1_clicked();
    void on_list_op_2_clicked();

    void on_add_op_2_clicked();

    void on_up_op_2_clicked();

    void on_del_op_2_clicked();
    void on_list_op_3_clicked();

    void on_add_op_3_clicked();

    void on_up_op_3_clicked();

    void on_del_op_3_clicked();
    void on_add_val_clicked();

private:
    Ui::MainWindow *ui;
    client myclient;
};
#endif // MAINWINDOW_H

• sources :

connexion.cpp :

#include "connexion.h"

connexion::connexion()
{

}
bool connexion::connect(){
bool test=false;
     QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
     db.setDatabaseName("ProjectDataBase");
     db.setUserName("eclipse");
     db.setPassword("eclipse");

     if (db.open())
     {
         test=true;
     }

 return  test ;
}

client.cpp :

#include "client.h"
// parameterized constructor
client::client(int cin , QString name , QString firstName , QString dob)
{
    this->cin = cin;
    this->name = name;
    this->firstName = firstName ;
    this->dob = dob ;
}
//default constructor
client::client()
{
    cin = 0;
    name = "";
    firstName = "";
    dob = "";
}

/* definition of getters */

int client::getCin(){
    return cin;
}
QString client::getName(){
    return name;
}
QString client::getFirstName(){
    return firstName;
}
QString client::getDateOfBirth(){
    return dob;
}
/* definition of setters */

void client::setCin(int cin){
    this->cin = cin ;
}
void client::setName(QString name){
    this->name = name  ;
}
void client::setFirstName(QString firstName){
    this->firstName = firstName  ;
}
void client::setDateOfBirth(QString dob){
    this->dob = dob ;
}
/* definition of CRUD */
/*DISPLAY*/
QSqlQueryModel * client::display_all_clients(){
    QSqlQueryModel *model = new QSqlQueryModel;
    model->setQuery("SELECT * FROM CLIENTS");
    if (model->lastError().isValid()) {
        qDebug() << "Error executing query:" << model->lastError().text();
    }
    model->setHeaderData(0, Qt::Horizontal, QObject::tr("IDENTIFIANT"));
    model->setHeaderData(1, Qt::Horizontal, QObject::tr("FIRST NAME"));
    model->setHeaderData(2, Qt::Horizontal, QObject::tr("NAME"));
    model->setHeaderData(3, Qt::Horizontal, QObject::tr("DATE OF BIRTH"));
    return model ;
}
/*ADD*/
bool client::add_client() {
    QSqlQuery query;
    query.prepare("INSERT INTO CLIENTS (CIN, FIRSTNAME, NAME, DOB) "
                  "VALUES (?, ?, ?, ?)");
    query.bindValue(0, cin);
    query.bindValue(1, firstName);
    query.bindValue(2, name);
    query.bindValue(3, dob);
    return query.exec();
}

/*DELETE*/
bool client::delete_client(int cin) {
    QSqlQuery query;
    query.prepare("DELETE FROM CLIENTS WHERE CIN = ?");
    query.bindValue(0, cin);
    return query.exec();
}

mainwindow.cpp :

#include "mainwindow.h"
#include "./ui_mainwindow.h"
#include "client.h"
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{

    ui->setupUi(this);
    ui->stackedWidget->setCurrentWidget(ui->home_page);
    qDebug() << QSqlDatabase::drivers();
    /*display clients opration*/
    ui->clients_table->setModel(myclient.display_all_clients());
    /*end of display clients opration*/
}

MainWindow::~MainWindow()
{
    delete ui;
}
/* insert client button*/
void MainWindow::on_add_val_clicked()
{
    int cin = ui->cin_in->text().toInt();
    QString name = ui->name_in->text();
    QString firstName = ui->firstname_in->text();
    QString dob = ui->dob_in->text();
    client myClient(cin,name,firstName,dob);
    bool operation_result = myClient.add_client();
    if(operation_result == true){
        std::cout << "insert done" << std::endl;
    }
    else{
        std::cout << "insert not done" << std::endl;
    }
}
/* endof insert client button*/
/*navigation bar operations*/
/*home page nav*/

void MainWindow::on_home_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->home_page);
}
void MainWindow::on_employees_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->employees_page);
}
void MainWindow::on_clients_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->clients_page);
}
void MainWindow::on_stock_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->stock_page);
}
void MainWindow::on_settings_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->settings_page);
}
void MainWindow::on_about_us_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->about_us_page);
}

/*employees page nav*/

void MainWindow::on_home_2_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->home_page);
}
void MainWindow::on_employees_2_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->employees_page);
}
void MainWindow::on_clients_2_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->clients_page);
}
void MainWindow::on_stock_2_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->stock_page);
}
void MainWindow::on_settings_2_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->settings_page);
}
void MainWindow::on_about_us_2_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->about_us_page);
}
/* employer operations*/
/*list page*/
void MainWindow::on_list_op_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->list);
}

void MainWindow::on_add_op_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->add);
}

void MainWindow::on_up_op_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->update);
}

void MainWindow::on_del_op_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->delet);
}
/*add page*/
void MainWindow::on_list_op_1_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->list);
}

void MainWindow::on_add_op_1_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->add);
}

void MainWindow::on_up_op_1_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->update);
}

void MainWindow::on_del_op_1_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->delet);
}
/*update page*/

void MainWindow::on_list_op_2_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->list);
}

void MainWindow::on_add_op_2_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->add);
}

void MainWindow::on_up_op_2_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->update);
}

void MainWindow::on_del_op_2_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->delet);
}
/*delete page*/
void MainWindow::on_list_op_3_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->list);
}

void MainWindow::on_add_op_3_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->add);
}

void MainWindow::on_up_op_3_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->update);
}

void MainWindow::on_del_op_3_clicked()
{
    ui->employees_operations->setCurrentWidget(ui->delet);
}
/*clients page nav*/

void MainWindow::on_home_3_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->home_page);
}
void MainWindow::on_employees_3_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->employees_page);
}
void MainWindow::on_clients_3_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->clients_page);
}
void MainWindow::on_stock_3_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->stock_page);
}
void MainWindow::on_settings_3_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->settings_page);
}
void MainWindow::on_about_us_3_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->about_us_page);
}
/*stock page nav*/

void MainWindow::on_home_4_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->home_page);
}
void MainWindow::on_employees_4_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->employees_page);
}
void MainWindow::on_clients_4_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->clients_page);
}
void MainWindow::on_stock_4_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->stock_page);
}
void MainWindow::on_settings_4_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->settings_page);
}
void MainWindow::on_about_us_4_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->about_us_page);
}
/*abouts us page nav*/

void MainWindow::on_home_5_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->home_page);
}
void MainWindow::on_employees_5_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->employees_page);
}
void MainWindow::on_clients_5_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->clients_page);
}
void MainWindow::on_stock_5_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->stock_page);
}
void MainWindow::on_settings_5_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->settings_page);
}
void MainWindow::on_about_us_5_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->about_us_page);
}
/*employees page nav*/

void MainWindow::on_home_6_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->home_page);
}
void MainWindow::on_employees_6_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->employees_page);
}
void MainWindow::on_clients_6_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->clients_page);
}
void MainWindow::on_stock_6_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->stock_page);
}
void MainWindow::on_settings_6_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->settings_page);
}
void MainWindow::on_about_us_6_clicked()
{
    ui->stackedWidget->setCurrentWidget(ui->about_us_page);
}

main.cpp

#include "mainwindow.h"
#include "connexion.h"
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
       connexion c;
       bool test=c.connect();
       if(test)
       {w.show();
           QMessageBox::information(nullptr, QObject::tr("database is open"),
                       QObject::tr("connection successful.\n"
                                   "Click Cancel to exit."), QMessageBox::Cancel);

   }
       else
           QMessageBox::critical(nullptr, QObject::tr("database is not open"),
                       QObject::tr("connection failed.\n"
                                   "Click Cancel to exit."), QMessageBox::Cancel);

    return a.exec();
}

[Christian Ehrlicher]

@eclispe So as I said. You execute a query before opening the database connection. Fix your code.

[eclispe]

Yeah @Christian-Ehrlicher , the issue is solved

thnak you @Christian-Ehrlicher ! and Thanks to all of you for your help with this problem; I truly appreciate your time and effort.

• This is the correct version of the code (not perfect but it works ) for anyone who may encounter the same problem :

connection.h :

#ifndef CONNEXION_H
#define CONNEXION_H
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>
class connexion
{
public:
    QSqlDatabase db ;
    connexion();
    bool connect();
    bool check_data_base();
};

#endif // CONNEXION_H

connexion.cpp :

#include "connexion.h"

connexion::connexion()
{

}
bool connexion::connect() {
    bool test = false;
    db = QSqlDatabase::addDatabase("QODBC");
    db.setDatabaseName("ProjectDataBase");
    db.setUserName("eclipse");
    db.setPassword("eclipse");

    if (db.open()) {
        test = true;
    }

    return test;
}

bool connexion::check_data_base(){
    if (db.isValid() && db.isOpen()) {
        return true;
    } else {
        return false;
    }
}

mainwindow.cpp :

#include "mainwindow.h"
#include "./ui_mainwindow.h"
#include "client.h"
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{

    ui->setupUi(this);
    ui->stackedWidget->setCurrentWidget(ui->home_page);
    qDebug() << QSqlDatabase::drivers();
    connexion c;
    c.connect();
    if (c.check_data_base()) {
            ui->clients_table->setModel(myclient.display_all_clients());
        } else {
            qDebug() << "database is not open";
        }
}

MainWindow::~MainWindow()
{
    delete ui;
}
//rest of code .. 

main.cpp :

#include "mainwindow.h"
#include "connexion.h"
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

[SGaist]

@eclispe one thing: don't keep a QSqlDatabase instance as member variables. It's all explained in the documentation why.

[eclispe]

@SGaist Roger that