Qt4/Qt-Creator Read MySql Table (Console Mode)

--D. Thiebaut 15:11, 24 February 2011 (EST)

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This tutorial illustrates how to use Qt Creator to write a simply program that accesses a MySql database and reads the contents of a table.

Setup

We assume that you have installed Qt Creator and Qt 4 on your Mac (or Windows/Linux platform).

Steps

• Follow the steps of the Hello World example, and create a project called mySqlSimpleTable.

• Enter the code below in main.cpp:

// mySqlSimpleTable project
// main.cpp
// D. Thiebaut
// This program accesses a MySql database server, opens up a
// connection to a database (called dummy), with user name
// "dummy" and password "xxxxxx", and reads the full contents
// of a table called "table1".
// The contents of the table is dumped on the console.
// Good information on Qt and QSqlQueries can be found here:
// http://doc.qt.nokia.com/latest/qsqlquery.html
// Table format:
//CREATE TABLE IF NOT EXISTS `table1` (
//  `Id` int(11) NOT NULL auto_increment,
//  `word` varchar(45) default NULL,
//  PRIMARY KEY  (`Id`)
//) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=4 ;
//

#include <QtCore/QCoreApplication>
#include <QtSql>
#include <qtextstream.h>
#include <iostream>

using namespace std;

int main(int argc, char *argv[]) {
    //--- use a QTextStream: it makes it easier to output ---
    //--- QString to cout.                                ---
    QTextStream cout(stdout, QIODevice::WriteOnly);

    //--- define the database connection ---
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
    db.setHostName("xgridmac.dyndns.org");  // host
    db.setDatabaseName("dummy");            // database
    db.setUserName("dummy");                // user
    db.setPassword("dummy");               // password

    //--- attempt to open it ---
    bool ok = db.open();

    if ( ok ) {
        //--- we're good! ---
        cout << "Database open\n";

        //--- run a query and print data returned ---
        QSqlQuery query( "select * from table1" );
        if ( !query.isActive() )
            cout << "Query Error" + query.lastError().text()
                 << endl;
        else while (query.next()) {
                int Id = query.value(0).toInt();
                QString word = query.value(1).toString();
                cout << QString( "%1\t%2\n").arg( Id).arg( word );
                }

        //--- add a new entry to the table ---
        query.prepare( "INSERT INTO table1 (Word) VALUES ( :word ) ");
        query.bindValue( ":word", "Banana" );
        query.exec();

        //--- close connection to database
        db.close();
    }
    else
        //--- something went wrong ---
        cout << "Error opening database\n";

    return 0;
}

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