QSQLite correct way to close and re-open

gfxx

He, need to close QSQlite DB .... update it ... and re open on app .... unfortunately I have some TableView open during these exchange ... so obtain these error ....

QSqlDatabasePrivate::removeDatabase: connection 'Db2' is still in use, all queries will cease to work.
/* lastError qDebug messages lasterror */  QSqlError("", "Driver not loaded", "Driver not loaded")

I close and re-open in these way (sorry for usleep, close your eyes on these) ....

void MainWindow::reopenDB(){

    QSqlDatabase Db2= QSqlDatabase::database("db2");
    Db2.close();
    Db2.removeDatabase("db2");
    qDebug() << "Db2 ... CLOSE DB... problem..." << Db2.lastError();
    usleep(100000);
    Db2 = QSqlDatabase::addDatabase("QSQLITE", "db2");
    Db2.setDatabaseName("/home/mypath/DB2.sqlite3");
    qDebug() << "Db2 ... REOPENdb... problem..." << Db2.lastError();

    if (!Db2.open())
    {
        QMessageBox msgBoxD2B;
        msgBoxD2B.setStyleSheet("background-color:gray");
        msgBoxD2B.setIcon(QMessageBox::Critical);
        msgBoxD2B.setWindowTitle("ERROR D.B.");
        msgBoxD2B.setText("Impossicle open db");
        msgBoxD2B.setInformativeText("Please restarat app");
        msgBoxD2B.setStandardButtons(QMessageBox::Ok);
        msgBoxD2B.setDefaultButton(QMessageBox::Ok);
        int retD2B = msgBoxD2B.exec();
        switch (retD2B) {
          case QMessageBox::Ok:
              break;
          default:
              break;
        }
    }
    else{

        Db2 = QSqlDatabase::database("Db2");
        usleep(50000);

        sqlViewF();
        sqlViewE();
    }
}

where are the problem that not see it??

real thanks

Christian Ehrlicher

@gfxx said in QSQLite correct way to close and re-open:

where are the problem that not see it??

You still have an instance of your db so it can't get closed.

QSqlDatabase::database("db2").close()
QSqlDatabase::removeDatabase("db2");

SGaist

Hi,

You have the explanation on how to do it in the method documentation.

gfxx

@Christian-Ehrlicher .... ok but my question was these at end .... istance active can become from tableview? Or better show data with a select query on tableview is a persistent istance? so for first need to clear tableview and after can close db? Because until now I think query for tableview can be consider a "oneshot" use of db ....when data is printed db work is end so can cloese it. Is not right?

Plus all my query is inside a specific void call everytime for a specific pourpose .... so think example:

{
    QSqlDatabase db = QSqlDatabase::database("sales");
    QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db);
}
// Both "db" and "query" are destroyed because they are out of scope
QSqlDatabase::removeDatabase("sales"); // correct

is equal to:

void Mainwindows::sales()
{
    QSqlDatabase db = QSqlDatabase::database("sales");
    QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db);
}

void Mainwindows::closeDB(){
// Both "db" and "query" are destroyed because they are out of scope
QSqlDatabase::removeDatabase("sales"); // correct
 }

thanks a lot

Christian Ehrlicher

@gfxx said in QSQLite correct way to close and re-open:

Because until now I think query for tableview can be consider a "oneshot" use of db ....when data is printed db work is end so can cloese it. Is not right?

You're not right - the QSqlTableModel holds the QSqlQuery and therefore a database connection.

gfxx

@Christian-Ehrlicher said in QSQLite correct way to close and re-open:

You're not right - the QSqlTableModel holds the QSqlQuery and therefore a database connection.

so seems to need to stop QSqlTableModel first .... than close db .... right?

JonB

@gfxx
You may have to delete the QSqlTableModel and then close and remove the database?

gfxx

@JonB is english grammar correction? Thanks ;)) if not ..... seems is what @Christian-Ehrlicher think .... at these point think better stategy can be update db only without close it ....

[premise:
my intent is read a db2 and show some table in a server PC, after via TCP need to copy entire db2 from a machine CLIENT that is a producer of data, than read again db2 on server and show again some table. Unfortunately all machinery use SQlite db. ]

maybe better stategy was copy from client to server db2(client side) as db2backup(server side) .... and update table from db2backup to db2 .... in these way need to delete QSqlTableModel during update operation?

JonB

@gfxx
No it was not a grammar correction, just what you may have to do to truly close the SQLite file database, which is what you asked.

If all you want to do is copy a file from client to server I do not see that you absolutely have to delete the QSqlTableModel prior to the operation. It might be advisable, but it may be sufficient to ensure that you have not previously done any updates to the file in the client.

Having said that, I think your code is a fair example of releasing the QSqlDatabase and then removing it anyway. But you must not then keep any QTableView around whose model is the QSqlTableModel.

gfxx

@JonB thanks a lot ... after these:

i try variuos scenario .... al least error become from that wrong code:

void MainWindow::showUploadDb(int pageIdx){


    QSqlDatabase::database("LavDb").close();  /* <- these the problem */

    closeDB();

/** my code */
}

after change these into these one:

void MainWindow::showUploadDb(int pageIdx){


    closeDB();

/** my code */
}

plus closeDB:

void MainWindow::closeDB(){
    stopChartF = true;  /* only a relais */ 
    QSqlDatabase::removeDatabase("Db2");
    QSqlDatabase::removeDatabase("g");  /* these is a therd db open for test pourpuse and hel me ... because no query on it at all */
    QTimer::singleShot(400, this, SLOT(reopenDB()));
}

plus reopenDB:

void MainWindow::reopenDB(){

    QSqlDatabase DB2= QSqlDatabase::addDatabase("QSQLITE", "Db2");
    DB2.setDatabaseName("/home/mypath/DB2.sqlite3");
    QSqlDatabase Dg = QSqlDatabase::addDatabase("QSQLITE", "g");
    Dg.setDatabaseName("/home/mypath/g.sqlite3");
    //qDebug() << "DB2 ... REOPENdb... problemi ..." << DB2.lastError();

    if (!Db2.open() || !Dg.open())
    {
        QMessageBox msgBoxD1B;
        msgBoxD1B.setStyleSheet("background-color:gray");
        msgBoxD1B.setIcon(QMessageBox::Critical);
        msgBoxD1B.setWindowTitle("ERROR D.B.");
        msgBoxD1B.setText("Impossibile connect to the world DB");
        msgBoxD1B.setInformativeText("restart");
        msgBoxD1B.setStandardButtons(QMessageBox::Ok);
        msgBoxD1B.setDefaultButton(QMessageBox::Ok);
        int retD1B = msgBoxD1B.exec();
        switch (retD1B) {
          case QMessageBox::Ok:

              break;
          default:
              // should never be reached
              break;
        }
    }
    else{

        Db2 = QSqlDatabase::database("Db2");
        Dg = QSqlDatabase::database("g");
        usleep(50000);
        stopChartF = false; /* only a relais */
        usleep(1000);

        sqlViewFupdate);
        sqlViewBupdate();
    }
}

all work as aspected and no error .... but these warning not understand at all ..... (remember "g" have not query at all, no table model or other view type at all, only db open ...)

QSqlDatabasePrivate::addDatabase: duplicate connection name 'Db2', old connection removed.
QSqlDatabasePrivate::addDatabase: duplicate connection name 'g', old connection removed.

why these .... In my opinion I close all correct, and reopen in correct way ... or not?

regards

jsulm

@gfxx said in QSQLite correct way to close and re-open:

QSqlDatabasePrivate::addDatabase: duplicate connection name 'Db2', old connection removed.
QSqlDatabasePrivate::addDatabase: duplicate connection name 'g', old connection removed.

Do you call addDatabase somewhere else (not only in reopenDB())?

gfxx

@jsulm yes here:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

QSqlDatabase DB2= QSqlDatabase::addDatabase("QSQLITE", "Db2");
    DB2.setDatabaseName("/home/mypath/DB2.sqlite3");
    QSqlDatabase Dg = QSqlDatabase::addDatabase("QSQLITE", "g");
    Dg.setDatabaseName("/home/mypath/g.sqlite3");

    if (!Db2.open() || !Dg.open())
    { /*  etc etc .... */

when start the app ..... so need to call only one time .... usign reopenDB() call from mainwindows too? good to know. Is these?

thanks

gfxx

@jsulm OK .... leave from void Minwindows::Mainwindows ..... open db command and unse only reopenDB call for that db and all work like a charm.

thanks a lot.