QSqlRelationalTableModel and complex queries

Panoss

I ended up using QAbstractTableModel, I think this is the one I need.
Now, let 's say I make a function getDataFromDB, and result set is stored in a QStringList (?? I don't know, I 'm asking, maybe you can suggest me what to use).

Then in ::data function, how shall I use this variable to return the data to the "user"? (I mean the QTableView that will use the data to display them)

VRonin

I'd suggest a QHash<quint64,QVariant> where the key has the most significant 32 bits as the row index and the least significant 32 as the column

Panoss

I 've made this function: (I call it of course, like this: model->setQuery("SELECT id, name FROM parts"))

 void TableModel::setQuery(const QSqlQuery &qry) {
     query = qry;
 }

I suppose this is not enough for the model to get the data from db and then be available (I mean the data from db) to the model? (a QAbstractTableModel)
Must I do something more?

And this is the data function:

 QVariant TableModel::data(const QModelIndex &index, int role) const
 {
     if (!index.isValid())
         return QVariant();
     if (index.row() >= query.size())
         return QVariant();
     if (role == Qt::DisplayRole) {
         query.seek(index.row());
         return query.value(index.column()); 
     } else {
         return QVariant();
     }
}

Where I get an error:
...\tablemodel.cpp:74: error: C2662: 'QSqlQuery::seek' : cannot convert 'this' pointer from 'const QSqlQuery' to 'QSqlQuery &'
Conversion loses qualifiers

It's at the line 'query.seek(index.row());'.

SGaist

How did you declared your query member variable ?

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:

make LEFT JOINS on the second table
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.