I'm trying to use a proxy model to take a 'parentId' column in a QSqlTableModel (using SQLITE) and view the hierarchy with a QTreeView. To make this work without needed a treeItem-type class I'm using internalId() from QModelIndex to store the 'parentId'. It works 99% of the time and I can't nail down where I'm messing up. I can view the parents/children and even expand/collapse them but I cannot select the children of a parent item. The selectionModel's selectionChanged() signal and the proxy models index() return the expected QModelIndex and so I don't know what is making the view upset. Here is the code that produces the issue. Thanks for any insight or suggestions

mainwindow.h
Qt Code: 
  1. #ifndef MAINWINDOW_H
  2. #define MAINWINDOW_H
  3.  
  4. #include <QMainWindow>
  5. #include <QSqlError>
  6.  
  7. class QTreeView;
  9. class sqlTreeModelTest;
  10.  
  11. class MainWindow : public QMainWindow
  12. {
  13.     Q_OBJECT
  14.  
  15. public:
  16.     explicit MainWindow(QWidget *parent = 0);
  17.     QSqlError initdb();
  18. private:
  19.     QTreeView *treeView;
  20.     void setupModel();
  21. };
  22.  
  23. #endif // MAINWINDOW_H
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mainwindow.cpp
Qt Code: 
  1. #include "mainwindow.h"
  2. #include "sqltreemodeltest.h"
  3. #include "proxytreemodeltest.h"
  4.  
  5. #include <QTreeView>
  6. #include <QVBoxLayout>
  7. #include <QSqlQuery>
  8.  
  9. MainWindow::MainWindow(QWidget *parent) :
  10.     QMainWindow(parent)
  11. {
  12.     QWidget     *centralWidget  = new QWidget(this);
  13.     QVBoxLayout *verticalLayout = new QVBoxLayout(centralWidget);
  14.     treeView = new QTreeView(centralWidget);
  15.     verticalLayout->addWidget(treeView);
  16.     setCentralWidget(centralWidget);
  17.  
  18.     QSqlError error = initdb();
  19.     if(error.isValid())
  20.         qDebug() << error.text();
  21.     setupModel();
  22. }
  23.  
  24. QSqlError MainWindow::initdb() {
  25.  
  26.     QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
  27.  
  28.     db.setDatabaseName(":memory:");
  29.     if(!db.open())
  30.         return db.lastError();
  31.  
  33.     QStringList tables = db.tables();
  34.     if(tables.contains("test", Qt::CaseInsensitive))
  35.         if(!q.exec("DROP TABLE test"))
  36.             return q.lastError();
  37.  
  38.     if(!q.exec(QLatin1String("CREATE TABLE test(id INTEGER PRIMARY KEY, title VARCHAR, type INTEGER, parentId INTEGER DEFAULT 0)")))
  39.         return q.lastError();
  40.     if(!q.exec(QLatin1String("INSERT INTO test (title, type, parentId)"
  41.                              "VALUES ('row0', 0, 0),"
  42.                                     "('row0a', 0, 1)")))
  43.         return q.lastError();
  44.     return QSqlError();
  45. }
  46.  
  47. void MainWindow::setupModel() {
  48.  
  49.     sqlTreeModelTest *testModel = new sqlTreeModelTest(this);
  50.     testModel->setTable("test");
  51.     testModel->select();
  52.  
  53.     proxyTreeModelTest *treeProxy = new proxyTreeModelTest(this);
  54.     treeProxy->setSourceModel(testModel);
  55.  
  56.     treeView->setModel(treeProxy);
  57.     treeView->setSelectionBehavior(QAbstractItemView::SelectRows);
  58.     treeView->setSelectionMode(QAbstractItemView::SingleSelection);
  59. }
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sqltreemodeltest.h
Qt Code: 
  1. #ifndef SQLTREEMODELTEST_H
  2. #define SQLTREEMODELTEST_H
  3.  
  4. #include <QSqlTableModel>
  5.  
  6. class sqlTreeModelTest : public QSqlTableModel
  7. {
  8.     Q_OBJECT
  9.  
  10. public:
  11.     sqlTreeModelTest(QObject *parent=0);
  12.     virtual Qt::ItemFlags flags(const QModelIndex &index) const;
  13. };
  14.  
  15. #endif // SQLTREEMODELTEST_H
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sqltreemodeltest.cpp
Qt Code: 
  1. #include "sqltreemodeltest.h"
  2.  
  3. sqlTreeModelTest::sqlTreeModelTest(QObject *parent) : QSqlTableModel(parent) {}
  4.  
  5. Qt::ItemFlags sqlTreeModelTest::flags(const QModelIndex &index) const {
  6.     //QSqlTableModel doesn't allow children so use these flags
  7.     if(index.isValid())
  8.         return Qt::ItemIsEnabled | Qt::ItemIsSelectable;
  9.     else
  10.         return 0;
  11. }
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proxytreemodeltest.h
Qt Code: 
  1. #ifndef PROXYTREEMODELTEST_H
  2. #define PROXYTREEMODELTEST_H
  3.  
  4. #include <QDebug>
  5. #include <QAbstractProxyModel>
  6.  
  7. class QSqlQuery;
  8.  
  9. class proxyTreeModelTest : public QAbstractProxyModel
  10. {
  11.     Q_OBJECT
  12.  
  13. public:
  14.     proxyTreeModelTest(QObject *parent=0);
  15.     virtual QModelIndex mapFromSource(const QModelIndex &sourceIndex) const;
  16.     virtual QModelIndex mapToSource(const QModelIndex &proxyIndex) const;
  17.     virtual QModelIndex parent(const QModelIndex &child) const;
  18.  
  19.     virtual QModelIndex index(int row, int column, const QModelIndex &parent) const;
  20.     virtual int rowCount(const QModelIndex &parent) const;
  21.     virtual int columnCount(const QModelIndex &parent) const { return sourceModel()->columnCount(parent); }
  22.  
  23.     virtual QVariant headerData(int section, Qt::Orientation orientation, int role) const { return sourceModel()->headerData(section,orientation,role); }
  24.     virtual bool setHeaderData(int section, Qt::Orientation orientation, const QVariant &value, int role) { return sourceModel()->setHeaderData(section,orientation,value,role); }
  25.  
  26.     virtual bool hasChildren(const QModelIndex &parent) const;
  27.  
  28. private:
  29.  
  30.     int getParentId(int childId) const;
  31.     QSqlQuery* getChildren(int parentId) const;
  32. };
  33.  
  34. #endif // PROXYTREEMODELTEST_H
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proxytreemodeltest.cpp
Qt Code: 
  1. #include "proxytreemodeltest.h"
  2.  
  3. #include <QSqlQuery>
  4. #include <QSqlTableModel>
  5. #include <QSqlError>
  6.  
  7. #include <QDebug>
  8.  
  9. proxyTreeModelTest::proxyTreeModelTest(QObject *parent) : QAbstractProxyModel(parent) {}
  10.  
  11. QModelIndex proxyTreeModelTest::mapFromSource(const QModelIndex &sourceIndex) const {
  12.     if(!sourceIndex.isValid())
  13.         return QModelIndex();
  14.  
  15.     int id = (sourceIndex.column() == 0) ? sourceIndex.data().toInt() : sourceIndex.sibling(sourceIndex.row(),0).data().toInt();
  16.  
  17.     int row = -1;
  18.     QSqlQuery* q = getChildren(getParentId(id));
  19.     while(q->next()) {
  20.         row++;
  21.         if(q->value(0).toInt() == id)
  22.             break;
  23.     }
  24.     delete q;
  25.     return createIndex(row, sourceIndex.column(), id);
  26. }
  27.  
  28. QModelIndex proxyTreeModelTest::mapToSource(const QModelIndex &proxyIndex) const {
  29.     if(!proxyIndex.isValid())
  30.         return QModelIndex();
  31.  
  32.     int id = proxyIndex.internalId();
  33.  
  35.     q.exec("SELECT id FROM test");
  36.     int row = -1;
  37.     while(q.next()) {
  38.         row++;
  39.         if(q.value(0).toInt() == id)
  40.             break;
  41.     }
  42.     return sourceModel()->index(row, proxyIndex.column());
  43. }
  44.  
  45. bool proxyTreeModelTest::hasChildren(const QModelIndex &parent) const {
  46.  
  48.     q.prepare("SELECT COUNT(*) FROM test WHERE parentId=?");
  49.     q.addBindValue(parent.internalId());
  50.     q.exec();
  51.     q.first();
  52.     return q.value(0).toInt() > 0;
  53. }
  54.  
  55. QModelIndex proxyTreeModelTest::parent(const QModelIndex &childIndex) const {
  56.  
  57.     int childId  = childIndex.internalId();
  58.     int parentId = getParentId(childId);
  59.     if(parentId == 0)
  60.         return QModelIndex();
  61.  
  62.     int parentRow = -1;
  63.     QSqlQuery* q = getChildren(getParentId(parentId));
  64.     while(q->next()) {
  65.         parentRow++;
  66.         if(q->value(0).toInt() == parentId)
  67.             break;
  68.     }
  69.     delete q;
  70.     return createIndex(parentRow, childIndex.row(), parentId);
  71. }
  72.  
  73. QModelIndex proxyTreeModelTest::index(int row, int column, const QModelIndex &parent) const {
  74.  
  75.     if(row < 0 || column < 0)
  76.         return QModelIndex();
  77.  
  78.     QSqlQuery* q = getChildren(parent.internalId());
  79.     q->seek(row);
  80.     int id = q->value(0).toInt();
  81.     delete q;
  82.     return createIndex(row, column, id);
  83. }
  84.  
  85. int proxyTreeModelTest::rowCount(const QModelIndex &parent) const {
  86.  
  87.     QSqlQuery* q = getChildren(parent.internalId());
  88.  
  89.     //use last() and at() since SQLite does not support query size calls
  90.     q->last();
  91.     int size = q->at() + 1;
  92.     delete q;
  93.     return size;
  94. }
  95.  
  96. int proxyTreeModelTest::getParentId(int childId) const {
  98.     q.prepare("SELECT parentId FROM test WHERE id=?");
  99.     q.addBindValue(childId);
  100.     q.exec();
  101.     q.first();
  102.     return q.value(0).toInt();
  103. }
  104.  
  105. QSqlQuery* proxyTreeModelTest::getChildren(int parentId) const {
  106.     QSqlQuery* q = new QSqlQuery;
  107.     q->prepare("SELECT id FROM test WHERE parentId=?");
  108.     q->addBindValue(parentId);
  109.     q->exec();
  110.     return q;
  111. }
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main.cpp
Qt Code: 
  1. #include "mainwindow.h"
  2. #include <QApplication>
  3.  
  4. int main(int argc, char *argv[])
  5. {
  6.     QApplication a(argc, argv);
  7.     MainWindow w;
  8.     w.show();
  9.  
  10.     return a.exec();
  11. }
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