void addSomething(QString queryString){
         query.exec(queryString);

And for SELECT queries i should use your solution with QDataWidgetMapper and QModel ?

It is not clear to me what you mean with security? The interface should not provide access to data which should be hidden and it does not matter how the interface is designed (whether you use one class per table or not). And who is "someone"? A developer using your interface or a real application user?

In the scenario you gave, i would still have to write a couple of methods for each of the tables and delete the unused method right ? I mean each table will still need methods for the queries.

Also what about security ? I am not really sure, but isn't easier for someone to have access to an admin table data (when he shouldn't), when these data are stored in a class that he already has access in ?

That will simplify your code.

@mrjj So, for every form (QT window) that needs to have access to the data, i have 2 classes. One to setup the interface/tables/lineEdits e.t.c and the other class contains the database stuff (db info, queries ).

This is an example of how my setup works for adding an entry to the table :

void Instruments::addInstrument(){
    QSqlQuery query(QSqlDatabase::database(connectionName));

    query.prepare("INSERT INTO " + databaseName + ".lab_instruments(id, serial_no, manufacturer, model, description, "
                  "comm_port, comm_baud_rate, comm_data_bits, comm_parity, comm_stop_bits, installation_date, "
                  "last_service, next_service) "
                  "VALUES(:id, :serial_no, :manufacturer, :model, :description, :comm_port, :comm_baud_rate, :comm_data_bits, "
                  ":comm_parity, :comm_stop_bits, :installation_date, :last_service, :next_service )");

    query.bindValue(":id", regNo);
    query.bindValue(":serial_no", serialNo);
    query.bindValue(":manufacturer", manufacturer);
    query.bindValue(":model", model);
    query.bindValue(":description", description);
    query.bindValue(":comm_port", commPort);
    query.bindValue(":comm_baud_rate", baudRate);
    query.bindValue(":comm_data_bits", dataBits);
    query.bindValue(":comm_parity", parity);
    query.bindValue(":comm_stop_bits", stopBits);
    query.bindValue(":installation_date", installDate);
    query.bindValue(":last_service", lastService);
    query.bindValue(":next_service", nextService);

    if(!query.exec()) { qDebug()<<query.lastError(); }

}

And this is the Qt method that handles the interface and calls this method :

void InstrumentsScreen::on_btnAdd_clicked()
{
    Instruments* instrument = new Instruments("addInstrument");

    //Extract data from text fields
    *instrument= updateValues(*instrument);
    //Update database
    instrument->connect();
    instrument->addInstrument();
    instrument->disconnect();
    QSqlDatabase::removeDatabase("addInstrument");
    initTable();
    on_btnClear_clicked();

}

Instruments InstrumentsScreen::updateValues(Instruments instrument){

    instrument.setRegNo(ui->txtRegNo->text());
    instrument.setSerialNo(ui->txtSerialNo->text());
    instrument.setManufacturer(ui->txtManufacturer->text());
    instrument.setModel(ui->txtModel->text());
    instrument.setDescription(ui->txtDescription->text());
    instrument.setCommPort(ui->txtCommPort->text());
    instrument.setBaudRate(ui->txtBaudRate->text());
    instrument.setDataBits(ui->txtDataBits->text());
    instrument.setParity(ui->cboxParity->currentText());
    instrument.setStopBits(ui->txtStopBits->text());
    instrument.setInstallationDate(ui->txtInstallDate->text());
    instrument.setLastService(ui->txtLastService->text());
    instrument.setNextService(ui->txtNextService->text());

}

So this is just for a button on one of the forms.

P.S: The reason for having each query in a method is because i feel like is bad programming having queries thrown all over the place in an interface class.

To add to @mrjj, are all your tables in a different database ?