Qt MySQL-创建新表

Question

I am new to QT programming so I am trying simple MySQL operations (Connecting, Building Database, Building table ...)

I used c# till now, so here I used similar construction (ie I put pushButton to run code and print out messages in editText arrea)

My "Connecting" code works perfectly, so does the "Building Database" code, but I have trouble creating the table.

1. My Working environment:
   • Win 7
   • QT Creator 3.4.1
   • Based on Qt 5.4.2
   • MySQL @ XAMPP v1.8.3

My Code:

void MainWindow::on_pushButton_2_clicked()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");

    db.setHostName("localhost");
    db.setDatabaseName("myTestDB");
    db.setUserName("root");
    db.setPassword("");

    if(db.open())  { ui->textBox->append("Connected..."); db.close(); }
    else ui->textBox->append(db.lastError().text());

    QSqlQuery query;
    query.prepare( "CREATE TABLE IF NOT EXISTS myTable (id INTEGER UNIQUE PRIMARY KEY, firstname VARCHAR(30), lastname VARCHAR(30))" );
    if(query.exec())
    {
        ui->textBox->append("Table created");
    }
    else
    {
        ui->textBox->append("Error");
        ui->textBox->append("MySQL error:" + query.lastError().text());
        ui->textBox->append("MySQL error code:"+ QString::number(query.lastError().number()));
    }
}

When I run code I get this response:
Connected...
Error
MySQL error:
MySQL error code:-1

So MySQL error is empty, and MySQL error code is -1
I also run SQL code directly to check for query errors
Thanks for any help and suggestions.

Answer 1

You close the database directly after connecting to it.

And you need to hand the db over to the query.

Change

if(db.open())  { ui->textBox->append("Connected..."); db.close(); }

QSqlQuery query;

to

if(db.open())  { ui->textBox->append("Connected..."); }

QSqlQuery query(db);

and then close the DB after the query.

It's your first question: Welcome to StackOverflow ;)