QSqlRelationalTableModel and complex queries

[Panoss]

private:

 QSqlQuery query;

I read from this:
"get rid of the const with const_cast"

What does this mean?

[VRonin]

"get rid of the const with const_cast"

NOOOOOOOOOOOOOOOOOOO!!!!
mutable QSqlQuery query; solves your compilation issue but I don't think your logic is going anywhere.

Just a second here. let's take a step back: what do you want to achieve?

• does the model need to be editable and changes be reflected in the database?
• will you have more than 1 column?

[Panoss]

I want my QTableView to display data from two tables.
This in SQL means my model should have the ability to:

1. make LEFT JOINS on the second table
2. Concatenate two fields.

For these things, QSqlQueryModel works fine.

But I also need to add and remove records, which QSqlQueryModel cannot do.

So, my conclusion is I should subclass QSqlQueryModel (this is what I'm doing right now, but I have problems...) and add custom functionality for adding and removing rows.

What do you think?

[VRonin]

Personally I would not subclass anything, I'd use a QStandardItemModel fill it with a QSqlQuery and react to QStandardItemModel::rowsInserted and QStandardItemModel::rowsRemoved signals to trigger the update in the db via another QSqlQuery

[Panoss]

The problem is I don't have the slightest idea how to do all this.
Is there some example I could look at?

EDIT: QStandardItemModel has no setQuery function.
How shall I "fill it with a QSqlQuery"?
You mean wit QStandardItemModel::setItem?

[VRonin]

@Panoss said in QSqlRelationalTableModel and complex queries:

How shall I "fill it with a QSqlQuery"

manually, outside the model

    model->removeRows(0, model->rowCount());
    model->removeColumns(0, model->columnCount());
    QSqlQuery testQuery;
    testQuery.prepare("select * from MyTable");
    if (testQuery.exec()) {
        for (bool firstRun = true; testQuery.next();) {
            const QSqlRecord currRecord = testQuery.record();
            if (firstRun) {
                firstRun = false;
                model->insertColumns(0, currRecord.count());
                for (int i = 0; i < currRecord.count(); ++i)
                    model->setHeaderData(i, Qt::Horizontal, currRecord.fieldName(i));
            }
            const int newRow = model->rowCount();
            model->insertRow(newRow);
            for (int i = 0; i < currRecord.count(); ++i)
                model->setData(model->index(newRow, i), currRecord.value(i));
        }
    }

[Panoss]

Works, the model->removeRow works, it removes a row from the model ,but how do I remove this row from the db too? Something like this?

QSqlQuery query;
    query.prepare("DELETE FROM MyTable WHERE id=1");
    if (query.exec()) {
etc. etc.

[SGaist]

You'll likely have to make a more precise delete query but otherwise, yes.

[Panoss]

What do you mean by "more precise"? I thought "WHERE id=1" makes it absolutely precise (the value "1" was chosen for the shake of the example).

[SGaist]

Sorry, that was badly written, I meant that you would have to ensure that you are passing the correct parameter(s) to the delete query to ensure you are deleting the same row in the database.

[Panoss]

Ah, ok, guys, VRonin, SGaist, thank you very much.

[VRonin]

be careful here as if you naively connect the database delete to rowsRemoved the first two lines:
(model->removeRows(0, model->rowCount()); model->removeColumns(0, model->columnCount());)
will delete your entire database and you cannot just use a QSignalBlocker on the model either or the view won't update

[kkmspb]

@Panoss Hi! I solved this problem. You can extended Qt sources. First you change QSqlRelationalTableModel in QSqlTabelModel style, i.e. you create qsqlrelationaltabelmodel_p.h file. Afterwards you can derive from QSqlRelationalTableModel and you wil get access to private data.

Than you rebuild qt souces.

Only you needs reimplement selectStatement.
(Sorry for my english). I'v done this on qt 4.8.1.