How to make a MySQL query in Qt? - c++

Question

I'm trying to create a simple app which allows user to enter a word and the app will output the definition. I have compiled words and definitions by making mysql database file. I thought using MySQL would be a faster way make my app. My database looks like this:
rowed | Column1(word) | Column2(definition)
1 DNA A double-stranded,helical...
The pseudocode for this program definitely should be like this:
if(lineEdit == wordInput)
{
ui->label->setText("Display definition)
}
I just can't figure out how to do it. So far I have tried following code:
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QMessageBox>
#include <QDebug>
#include <QPalette>
#define Path_to_DB "/Users/makkhay/Desktop/nep_eng-2.sqlite"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
// Set background picture
QPixmap bkgnd("/Users/makkhay/Desktop/background.jpg");
bkgnd = bkgnd.scaled(this->size(), Qt::IgnoreAspectRatio);
QPalette palette;
palette.setBrush(QPalette::Background, bkgnd);
this->setPalette(palette);
myDB = QSqlDatabase::addDatabase("QSQLITE");
myDB.setDatabaseName(Path_to_DB);
QFileInfo checkFile(Path_to_DB);
if(checkFile.isFile())
{
if(myDB.open())
{
ui->label->setText("The database is connected");
}
}else{
ui->label->setText("No file found!");
}
}
MainWindow::~MainWindow()
{
delete ui;
myDB.close();
}
void MainWindow::on_pushButton_clicked()
{
// QMessageBox::StandardButton reply= QMessageBox::question(this,
// "My Title", " Word not found, quit app?",
// QMessageBox::Yes | QMessageBox::No);
// if(reply == QMessageBox::Yes){
// QApplication::quit();
//}
if(!myDB.isOpen()){
qDebug() << " No connection to db";
return;
}
QString wordInput, definition;
wordInput = ui->lineEdit->text();
QSqlQuery qry;
qry.prepare("SELECT Column1,Column2 FROM Nepali WHERE Column1 = :input");
qry.bindValue(":input",wordInput);
// int fieldNo = query.record().indexof("Column1");
if(qry.exec())
{
ui->debug->setText(" Checking output!"); // output is visible
while (qry.next())
{
ui->output->setText("Checing output!"); // output is not visible
QString inputWord = qry.value(0).toString();
QString wordDefinition = qry.value(1).toString();
ui->output->setText(wordDefinition);
}
}
}

Answer 1

OK, the following code works for me. Try commenting out your existing code and pasting this code in. This code is basically the exact same code you posted, I just commented out some of the code to set the background and removed some excess lines.
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QMessageBox>
#include <QDebug>
#include <QPalette>
#include <QSqlQuery>
#include <QFileInfo>
#define Path_to_DB "/Users/makkhay/Desktop/nep_eng-2.sqlite"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
// Set background picture
//QPixmap bkgnd("/Users/makkhay/Desktop/background.jpg");
//bkgnd = bkgnd.scaled(this->size(), Qt::IgnoreAspectRatio);
//QPalette palette;
//palette.setBrush(QPalette::Background, bkgnd);
//this->setPalette(palette);
myDB = QSqlDatabase::addDatabase("QSQLITE");
myDB.setDatabaseName(Path_to_DB);
QFileInfo checkFile(Path_to_DB);
if(checkFile.isFile())
{
if(myDB.open())
{
ui->label->setText("The database is connected");
}
}else{
ui->label->setText("No file found!");
}
}
MainWindow::~MainWindow()
{
delete ui;
myDB.close();
}
void MainWindow::on_pushButton_clicked()
{
if(!myDB.isOpen()){
qDebug() << " No connection to db";
return;
}
QString wordInput;
wordInput = ui->lineEdit->text();
QSqlQuery qry;
qry.prepare("SELECT Column1,Column2 FROM Nepali WHERE Column1 = :input");
qry.bindValue(":input",wordInput);
if(qry.exec())
{
ui->debug->setText(" Checking output!");
while (qry.next())
{
// Retrieve Values from select statement
QString inputWord = qry.value(0).toString();
QString wordDefinition = qry.value(1).toString();
// Display values
ui->output->setText(wordDefinition);
}
} else {
qDebug() << "query failed to execute";
}
}

Answer 2

After declaring the qry variable the code should look like this:
qry.prepare("SELECT Column1,Column2 FROM tableName WHERE Column1 = :input");
qry.bindValue(":input",wordInput);
if(qry.exec())
{
if (qry.next())
{
// Extract the results from the SELECT statement
QString inputWord = qry.value(0).toString();
QString wordDefinition = qry.value(1).toString();
// Then use the values for whatever you wish.
}
}

Answer 3

You don't need comma before WHERE. Also, I guess that you are comparing Column1 with wordInput, not Column2.
if(qry.exec("SELECT Column1,Column2 FROM some_table WHERE Column1='"+ wordInput+"'"))
Edit: you don't mention a table you are selecting from.