QSqlDatabase warning message

[gabor53]

Hi,
I use the following to connect to a db:

db = QSqlDatabase::addDatabase ("QSQLITE","What");
        db.setDatabaseName (fileQstring );

When I'm done using the database I close the connection using

QSqlDatabase::removeDatabase ("What");

I keep getting the following warning message in Application Output:
"QSqlDatabasePrivate::removeDatabase: connection 'What' is still in use, all queries will cease to work."
What am I missing that causes this message?
Thank you.

[jsulm]

You probably have open queries. Check in the documentation (http://doc.qt.io/qt-5.6/qsqldatabase.html#removeDatabase):
"Warning: There should be no open queries on the database connection when this function is called, otherwise a resource leak will occur."

[SGaist]

Hi,

To add to @jsulm, is your db object a member of one of your class ? If so, then there's your problem. You don't have to keep such an object around especially if you only use the default connection.

[gabor53]

@SGaist
I defined the db in additem.h:

QSqlDatabase db;

so I assume its is part of the additem class. Should I just define it in additem.cpp?
I think my code follows the documentation, but I still get the error message
"QSqlDatabasePrivate::removeDatabase: connection 'Material' is still in use, all queries will cease to work".

       {
           db = QSqlDatabase::addDatabase ("QSQLITE","Material");
           db.setDatabaseName (fileQstring );

           if(!db.open ())
           {
               qDebug() << "The database is NOT open! (Material)";
           }
           else
           {
               qDebug() << "The database is open (Material)!";
           }

           QSqlQuery query_material ("SELECT Material FROM MaterialTable ORDER BY Material asc",db);

           if(query_material.isActive()==true)
           {
               qDebug() << "The query is active (Material).";
           }
           else
           {
               qDebug() << "The query is NOT active (Material).";
           }

           while (query_material.next ())
           {

               material = query_material.value(0).toString();

               ui->Material_Combo->addItem(material);
           }


           material = ui->Material_Combo->currentText ();

           if(material.isEmpty ())
           {
               qDebug() << "Material is empty!!!" ;
           }
           qDebug() << "Material in loop: " << material;
           db.close ();
       }
       QSqlDatabase::removeDatabase ("Material");
       ui->Material_Combo->clearEditText ();
       connect (ui->Material_Combo,SIGNAL(currentIndexChanged(int)),this,SLOT(getMaterial(int)));

What should I do to stop the error message? Which query is still running?
Thank you.

[the_]

@gabor53

You need to add the database connection only once, for example in your class constructor

AddItem::AddItem(QString fileQString) { //I dont know how it really looks like :)
  QSqlDatabase db = QSqlDatabase::addDatabase ("QSQLITE","Material");
  db.setDatabaseName (fileQstring );
  if(!db.open()) 
    //do some error handling here
}

Then in your other functions where you need to do some database thingies:

void AddItem::somefunction() {
 QSqlDatabase db = QSqlDatabase::database("Material");
  //the database is still open if you did not close it somewhere else, and the databaseName is still what you set
  QSqlQuery q("",db);
  q.prepare("select * from mytable"); // or whatever you need to do
//...
}

And finally, close the database and remove it in the descturctor

void AddItem::closedbcon() {
  QSqlDatabase db = QSqlDatabase::database("Material");
  db.close();
}

AddItem::~AddItem() {
  closedbcon();
  QSqlDatabase::removeDatabase ("Material");
}

[SGaist]

To add to @the_ , if you only have one database connection and don't give it a name, it becomes the default connection and you don't need to call QSqlDatabase::database each time you make a query.