Map table to tree through model/view possible?

[JD2000]

Ah, good point.

You certainly end up with a table and tree, both referencing the data held in the table and both having 4 rows (in this case) but yes, each table row becomes a tree column 0 element.

My take on this was as stated in the title - map a table to a tree - I don't know whether the parent child relationship between table row elements is actually that important. It makes a great intellectual exercise though, well solved!

[Davor]

Ah, good point.

You certainly end up with a table and tree, both referencing the data held in the table and both having 4 rows (in this case) but yes, each table row becomes a tree column 0 element.

My take on this was as stated in the title - map a table to a tree - I don't know whether the parent child relationship between table row elements is actually that important. It makes a great intellectual exercise though, well solved!

On the importance: currently, Qt framework doesn't allow any direct mapping between one table and a hierarchical structure. That's unfortunate, at least because both structures are isomorphic. Here a practical example: Suppose you gather data which is hierarchically representable, store it into a relational database (see my other post, here for reference: Kaufmann's Joe Celko's Trees and Hierarchies in SQL for Smarties) and which you want to reproduce/visualize. From such databases you only get tables... no trees.

The whole problem isn't solved yet: you still have redundant trees: take the following table of primary keys forming the edges between two nodes (i.e. two other tables):
11
12
23

Both 1 and 2 from the second row refer tot the same PK from the first column, so they should form one tree with two children.

Tree should look something like this:
1
|||1
|||2
2
|||3

Such tables are simple to generate with relational databases. What is needed is some way to translate them into trees. Wysota has made the first step. I will not bother him for the second, but just note this as an answer to your question.

And as for how to make it.... unfortunately it is not that easy again. The most important is the fact that the parent is uniquely identified by the preceding (primary key) fields (and not by the column and it's PK, as it would seem from the relational model).

Here is an example on how to populate the tree:

for each row
---for each column
------check column = primary
------PK = readPKfrommodel(row,column)
------append PK into PathIDVector (which is the parent's ID)
------If PathIDVector does not exist yet --> make a treeitem(PathIDVector) which is the child of treeitem(PathIDVector_less_one)

Currently I have this with TreeItem/TreeModel, and it's no pretty code. If I find time, I'll try to implement it in wysota's code, and post it here.

[JD2000]

Tables and trees are not isomorphic, that is the problem.

A tree holds what are essentially tables (their elements are indexed by [row,column]) in some sort of

hierarchy. If you collapse a tree, you end up with a table.

In order to impose such a hierarchy on a table, the table / table elements need to store their

row/column data as usual plus references to their parents. Then when you rebuild the tree check this

reference to find out which node to attach the table element to.

Alternatively for example in cases like yours where there is a defined structure, the parent reference

is not needed because it can be calculated by the model being used:

#include <QtGui>
 
int main(int argc, char **argv) {
    QApplication app(argc, argv);
 
    int maxrows = 4;
    int maxcols = 4;
 
    QStandardItemModel tableModel(maxrows, maxcols);
    for (int row = 0; row < maxrows; ++row) {
        for (int column = 0; column < maxcols; ++column) {
             QStandardItem *item = new QStandardItem(QString("row %0, column %1").arg(row).arg(column));
             tableModel.setItem(row, column, item);
        }
    }
 
    QTableView tablev;
    tablev.setModel(&tableModel);
    tablev.show();
 
    QStandardItemModel treeModel;
    QStandardItem *parentItem = treeModel.invisibleRootItem();
 
    for (int row = 0; row < maxrows; ++row) {
        for (int col = 0; col < maxcols; ++col) {
           // grab the data out of the table
            QStandardItem *item = new QStandardItem(tableModel.data(tableModel.index(row, col, QModelIndex()), Qt::DisplayRole).toString());
            parentItem->appendRow(item);
            parentItem = item;
        }
    parentItem = treeModel.invisibleRootItem();
    }
 
    QTreeView treev;
    treev.setModel(&treeModel);
    treev.show();
 
    return app.exec();
 
}

#include <QtGui>

int main(int argc, char **argv) {
    QApplication app(argc, argv);

    int maxrows = 4;
    int maxcols = 4;

    QStandardItemModel tableModel(maxrows, maxcols);
    for (int row = 0; row < maxrows; ++row) {
        for (int column = 0; column < maxcols; ++column) {
             QStandardItem *item = new QStandardItem(QString("row %0, column %1").arg(row).arg(column));
             tableModel.setItem(row, column, item);
        }
    }

    QTableView tablev;
    tablev.setModel(&tableModel);
    tablev.show();

    QStandardItemModel treeModel;
    QStandardItem *parentItem = treeModel.invisibleRootItem();

    for (int row = 0; row < maxrows; ++row) {
        for (int col = 0; col < maxcols; ++col) {
           // grab the data out of the table
            QStandardItem *item = new QStandardItem(tableModel.data(tableModel.index(row, col, QModelIndex()), Qt::DisplayRole).toString());
            parentItem->appendRow(item);
            parentItem = item;
        }
    parentItem = treeModel.invisibleRootItem();
    }

    QTreeView treev;
    treev.setModel(&treeModel);
    treev.show();

    return app.exec();

}

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The problem here is that after creation, the tree and table are independant of each other.

I suppose that they could be kept in sync by implementing their respective data changed signals/slots.

[wysota]

I suppose that they could be kept in sync by implementing their respective data changed signals/slots.

Oh, I would really like to see you do that... Especially the part where items are added or removed.

[JD2000]

I had not given it much thought to be honest, presumably in that case you would use the rows/columns inserted or removed signals. I was actually trying to respond to the

On the importance: currently, Qt framework doesn't allow any direct mapping between one table and a hierarchical structure. That's unfortunate, at least because both structures are isomorphic. Here a practical example .........

comment. I think it is a bit unfair to expect QT to provide a mapping between a 2D table and a 3D tree framework, infact it is impossible without some extra information relating to the structure of the tree.

I note that you are no longer a guru, congratulations on your enlightenment Wysota!