Why does isOpen() function always return true? - database

Question

In my constructor(qt 5.4.1 - windows 7):
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName(":memory:");
db.open();
QSqlQuery q;
q.exec("create table authors(num integer, birthdate date)");
q.exec("insert into authors values('123', '2015-01-01')");
qDebug()<<"your info saved in db.";
Every things is okay until now but, later, I need to change my db and save some date permanently, so:
int Dialog::SaveInfosPermanent()
{
QSqlDatabase::database().close();
if ( QSqlDatabase::database().isOpen ()) {
qDebug()<<"DB is open.";
return 1;
}
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName("newDB.db");
db.open();
QSqlQuery q;
q.exec("create table authors(num integer, birthdate date)");
q.exec("insert into authors values('123', '2015-01-01')");
qDebug()<<"your info saved in db.";
return 0;
}
and output:
your info saved in db.
QSqlError("", "", "")
DB is open.
So what am I doing wrong? or there is better other ideas for changing db from memory to hard disk if user select a certain checkbox?

Answer 1

For me the best way to initialize db connection is to use connection name:
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE", connectionName);
With connection name you have some extra opportunity.
Removing database from the list of database connections, find docs here:
QSqlDatabase::removeDatabase(connectionName);
Get access to your database by name, find docs here:
QSqlDatabase db = QSqlDatabase::database(connectionName);
In your case use removeDatabase() with connection name, but don't forget about scope of db. See example at link i attach.
You can also use db with the same name in both case, as docs says:
Adds a database to the list of database connections using the driver
type and the connection name connectionName. If there already exists a
database connection called connectionName, that connection is removed.
The database connection is referred to by connectionName. The newly
added database connection is returned.