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Simple Qt4 and PostgreSQL book catalog application

08 Sep

For this current project we shall create a basic book storage application using the QT toolkit and PostgreSQL.Download and install QT   http://qt.nokia.com/products/developer-tools/  it comes with its own IDE qtcreator which we shall use for the actual work although any text editor can be used.Though that would unnecessarily prolong the length of the project.

Download and install the PostgreSQL database and configure it for use http://www.yolinux.com/TUTORIAL/LinuxTutorialPostgreSQL.html gives a good rundown if you are working on the linux platform.

Step1.Select the creation of  a new project.In the projects selection choose Qt4 Gui Application.Select the location and name of the project and in the required modules include the QtSql module.

Step2.Select forms from the Navmenu and open up the mainwindow.ui for editing.Design the layout of your app by using the available widgets.In this case we select LineEdit for the input.change their object names to something meaningful.Select pushbuttons and drag onto the workspace , give them useful names.

Step3.The design phase is now over and we shall proceed to coding the internals.Switch to Signal/Slot edit mode(F4).Direct the signals from the buttons to the main layout.In the configure connection pop-up select edit and add 3 new slots one each for clear , add and search.Link the clicked() action to our newly created slots.

Step4.Select the headers and in mainwindow.h add private slots addpub() , clearpub() and searchpub().In the protected section we shall add an auxillary function openDB() for establishing the database connection.In the private section we add a QSqlDatabase object db.

private slots:
void addpub();
void clearpub();
void searchpub();

protected:
void changeEvent(QEvent *e);
bool openDB();

private:
Ui::MainWindow *ui;
QSqlDatabase db;

Step5.We define the functions from step 4 , establishing the connection and inserting records with addpub() , searching for a particular record with searchpub() and clearing the form entries using clearpub().

-openDB function to connect to the database:

bool MainWindow::openDB()
{
db  = (QSqlDatabase::addDatabase(“QPSQL”));
db.setHostName(“localhost”);
db.setDatabaseName(“storagebox”);
db.setUserName(“noob”);
bool ret = db.open();
return ret;
}

-addpub function to insert from the form to the database

void MainWindow::addpub()
{

QString args = “INSERT INTO shelf VALUES (‘ “;;
bool ret = false;
bool lck = false;

args.append(ui->titleline->text()); args.append(“‘,'”);
args.append(ui->authorline->text()); args.append(“‘,'”);
args.append(ui->publisherline->text()); args.append(“‘,'”);
args.append(ui->isbnline->text()); args.append(“‘,'”);
args.append(ui->genreline->text()); args.append( ” ‘); “);

if(!db.isOpen())
{
lck = MainWindow::openDB();
}
ui->resultline->setText(“Pub insertion starting”);
if( lck )
{
ui->resultline->setText(“Pub is being inserted”);
QSqlQuery query;
ret = query.exec(args);

if(ret)
{
qDebug() <<“Pub has been inserted”;
ui->resultline->setText(“Pub has been inserted”);
}

}

}

-searchpub function to search for a stored record:

void MainWindow::searchpub()
{
bool ret = false;

if(!db.isOpen())
{
ret = MainWindow::openDB();
}

QString outLine;
QString findr;
QSqlQuery que;
findr = “select * from shelf where “;   findr += ui->srcq->currentText();   findr += ” like ‘%”;
findr += ui->searchline->text();        findr += ” %’ ;”;
if (ret)
{

que.exec(findr);

if( que.next())
{
outLine = que.value(0).toString();  outLine +=”\n”;
outLine.append(que.value(1).toString());    outLine +=”\n”;
outLine.append(que.value(2).toString());    outLine +=”\n”;
outLine.append(que.value(3).toString());    outLine +=”\n”;
outLine.append(que.value(4).toString());    outLine +=”\n”;

ui->textEdit->setText(outLine);
}
else
{
ui->textEdit->setText(“No result found”);
}

}

Step6.At this point you are ready to compile and run your application.

To download the project files used in this example  https://bitbucket.org/ar119/dbproject/get/f1dbf7bca3cd.zip

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1 Comment

Posted by on September 8, 2010 in code

 

Tags: , , ,

One response to “Simple Qt4 and PostgreSQL book catalog application

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