QTableView from SQLite, empty!

[grellsworth]

1)

Does "model" still exist when you show the table view?

Yes, "model" is defined in the class I use for sql code:

class SQLiteDB : public QObject
{
   Q_OBJECT
 
   public:
   // Constructors and ~Destructors
      SQLiteDB();
      virtual ~SQLiteDB();
 
   // Public Members
      QSqlRelationalTableModel model;
...
};

class SQLiteDB : public QObject
{
   Q_OBJECT

   public:
   // Constructors and ~Destructors
      SQLiteDB();
      virtual ~SQLiteDB();

   // Public Members
      QSqlRelationalTableModel model;
...
};

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2)

Where does "trackView" come from?

I created my user interface using Qt's Designer. trackView is a QTableView that I added to my layout in Designer:

= FROM ui_mymuse.h =

class Ui_MainWindow
{
public:
... some widgets ...
   QWidget *centralwidget;
   QTableView *trackTable;
... later ...
   void setupUi(QMainWindow *MainWindow)
   {
      centralwidget = new QWidget(MainWindow);
      trackTable = new QTableView(centralwidget);
   }
};

class Ui_MainWindow
{
public:
... some widgets ...
   QWidget *centralwidget;
   QTableView *trackTable;
... later ...
   void setupUi(QMainWindow *MainWindow)
   {
      centralwidget = new QWidget(MainWindow);
      trackTable = new QTableView(centralwidget);
   }
};

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3)

Are you sure it is the same QTableView as the one you see?

Yes, I've tried hiding/showing it in my code by using trackTable->hide() and trackTable->show() and that works correctly.

[jacek]

You first create the model and then the QSqlDatabase instance. Qt might not like this.

You can change SQLiteDB::createConnection() into a static method and invoke it before you instantiate SQLiteDB.

[grellsworth]

You first create the model and then the QSqlDatabase instance. Qt might not like this.

You can change SQLiteDB::createConnection() into a static method and invoke it before you instantiate SQLiteDB.

First of all, a BIG Thank you to jacek, for trying to help... I have had a little bit more success. My table comes up now with columns and rows, but they have no information in them, this is an improvement over a totally empty QTableView.

I tried totally getting rid of my SQLiteDB calls, and doing all the code in one place, in my initMainWidow function (which gets called by my MainWindow contructor).

Here's my code as it stands right now:

void MainWindow::initMainWindow()
{
   settings = new QSettings(APPNAME, DEVNAME);
 
   QString dbName = ":memory:";
 
   QSqlDatabase database = QSqlDatabase::addDatabase("QSQLITE");
   database.setDatabaseName(dbName);
 
   if(!database.open())
   {
      QMessageBox::critical(NULL, qApp->tr("Cannot open database"),
         qApp->tr("Unable to establish a connection with database '%1'.")
         .arg(dbName),
         QMessageBox::Cancel);
 
         return;
   }
 
   QSqlQuery query;
   if(!query.exec("create table tracks (id integer primary key autoincrement, artist varchar(50), "
      "title varchar(80), rating integer, status integer)"))
   {
      printf("Error 1\n");
   }
   else
   {
      printf("OK 1\n");
   }
   if(!query.exec("insert into tracks (artist, title, rating, status) values ('The Rolling Stones', 'Satisfaction', 33, 1)"))
   {
      printf("Error 2\n");
   }
   else
   {
      printf("OK 2\n");
   }
   if(!query.exec("insert into tracks (artist, title, rating, status) values ('The Doors', 'Riders on the Storm', 75, 1)"))
   {
      printf("Error 3\n");
   }
   else
   {
      printf("OK 3\n");
   }
   query.next();
 
   QSqlRelationalTableModel model;
 
   model.setTable("tracks");
   model.setEditStrategy(QSqlTableModel::OnManualSubmit);
   model.select();
 
   setTable(&model);
}
 
void MainWindow::setTable(QSqlTableModel *tblModel)
{
   trackTable->setModel(tblModel);
   trackTable->setItemDelegate(new QSqlRelationalDelegate(trackTable));
   trackTable->show();
}

void MainWindow::initMainWindow()
{
   settings = new QSettings(APPNAME, DEVNAME);

   QString dbName = ":memory:";

   QSqlDatabase database = QSqlDatabase::addDatabase("QSQLITE");
   database.setDatabaseName(dbName);

   if(!database.open())
   {
      QMessageBox::critical(NULL, qApp->tr("Cannot open database"),
         qApp->tr("Unable to establish a connection with database '%1'.")
         .arg(dbName),
         QMessageBox::Cancel);

         return;
   }

   QSqlQuery query;
   if(!query.exec("create table tracks (id integer primary key autoincrement, artist varchar(50), "
      "title varchar(80), rating integer, status integer)"))
   {
      printf("Error 1\n");
   }
   else
   {
      printf("OK 1\n");
   }
   if(!query.exec("insert into tracks (artist, title, rating, status) values ('The Rolling Stones', 'Satisfaction', 33, 1)"))
   {
      printf("Error 2\n");
   }
   else
   {
      printf("OK 2\n");
   }
   if(!query.exec("insert into tracks (artist, title, rating, status) values ('The Doors', 'Riders on the Storm', 75, 1)"))
   {
      printf("Error 3\n");
   }
   else
   {
      printf("OK 3\n");
   }
   query.next();

   QSqlRelationalTableModel model;

   model.setTable("tracks");
   model.setEditStrategy(QSqlTableModel::OnManualSubmit);
   model.select();

   setTable(&model);
}

void MainWindow::setTable(QSqlTableModel *tblModel)
{
   trackTable->setModel(tblModel);
   trackTable->setItemDelegate(new QSqlRelationalDelegate(trackTable));
   trackTable->show();
}

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So now I get a QTableView that looks like this:

-------------------------------------
   | 1 | 2 | 3 | 4 | 5 |
-------------------------------------
 1 |   |   |   |   |   |
-------------------------------------
 2 |   |   |   |   |   |
-------------------------------------

-------------------------------------
   | 1 | 2 | 3 | 4 | 5 |
-------------------------------------
 1 |   |   |   |   |   |
-------------------------------------
 2 |   |   |   |   |   |
-------------------------------------

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The fact that I get five columns and two rows is promising, at least it sees that I have two records with five fields each, but why aren't the cells being populated with data?

Sincerely,

Gordon E.

[jacek]

QSqlRelationalTableModel model;

model.setTable("tracks");
model.setEditStrategy(QSqlTableModel::OnManualSubm it);
model.select();

setTable(&model);

You create the model on the stack, so it gets destroyed as soon as it goes out of scope, leaving a dangling pointer behind. Better create that model on the heap (i.e. using the new operator).

[grellsworth]

You create the model on the stack, so it gets destroyed as soon as it goes out of scope, leaving a dangling pointer behind. Better create that model on the heap (i.e. using the new operator).

Yeah, it works now... so I guess you have to follow the following (undocumented) rules:

1) You must create your database connection before you create your (QSqlRelatinoalTableModel) model.
2) You must create your QSqlRelationalTableModel object on the heap, using the 'new' operator.

Did I miss anything?

[jacek]

2) You must create your QSqlRelationalTableModel object on the heap, using the 'new' operator.

Not exactly. You can create it on the stack, but you must make sure it exists long enough.

[grellsworth]

OK, so it should be:

2) Make sure your QSqlRelationalTableModel object doesn't go out of scope.

[jacek]

OK, so it should be:

2) Make sure your QSqlRelationalTableModel object doesn't go out of scope.

Yes, but this isn't something that must be documented.