//---------------------------------------------------------------------
        // CHANGED: CR39 (Split and merge complete messages)
        // Return true or false success so the main class knows
        // whether to notify the user following the completion of
        // the merge.
        //
        private bool PerformPhysicalMerge()
        {
            bool success = true;
            try
            {
                HluDataSet.incid_mm_polygonsDataTable selectTable = new HluDataSet.incid_mm_polygonsDataTable();
                _viewModelMain.GetIncidMMPolygonRows(ViewModelWindowMainHelpers.GisSelectionToWhereClause(
                    _viewModelMain.GisSelection.Select(), _viewModelMain.GisIDColumnOrdinals,
                    ViewModelWindowMain.IncidPageSize, selectTable), ref selectTable);

                if (selectTable.Count == 0)
                    return false;
                else if (selectTable.Count != _viewModelMain.GisSelection.Rows.Count)
                    throw new Exception(String.Format("GIS Layer and database are out of sync:\n{0} map polygons, {1} rows in table {2}.",
                        _viewModelMain.FragsSelectedMapCount, selectTable.Count, _viewModelMain.HluDataset.incid_mm_polygons.TableName));

                // lowest toid_fragment_id in selection assigned to result feature
                string newToidFragmentID = selectTable.Min(r => r.toid_fragment_id);

                if (selectTable.GroupBy(r => r.incid).Count() == 1)
                {
                    int minFragmID = Int32.Parse(newToidFragmentID);
                    _mergeResultFeatureIndex = selectTable.Select((r, index) =>
                        Int32.Parse(r.toid_fragment_id) == minFragmID ? index : -1).First(i => i != -1);
                }
                else
                {
                    _mergeFeaturesWindow = new WindowMergeFeatures();
                    _mergeFeaturesWindow.Owner = App.Current.MainWindow;
                    _mergeFeaturesWindow.WindowStartupLocation = WindowStartupLocation.CenterOwner;

                    _mergeFeaturesViewModelPhysical = new ViewModelMergeFeatures
                        <HluDataSet.incid_mm_polygonsDataTable, HluDataSet.incid_mm_polygonsRow>(selectTable,
                        _viewModelMain.GisIDColumnOrdinals, _viewModelMain.IncidTable.incidColumn.Ordinal,
                        null, _viewModelMain.GISApplication);
                    _mergeFeaturesViewModelPhysical.DisplayName = "Select Feature To Keep";
                    _mergeFeaturesViewModelPhysical.RequestClose += new ViewModelMergeFeatures
                        <HluDataSet.incid_mm_polygonsDataTable, HluDataSet.incid_mm_polygonsRow>
                        .RequestCloseEventHandler(_mergeFeaturesViewModelPhysical_RequestClose);

                    _mergeFeaturesWindow.DataContext = _mergeFeaturesViewModelPhysical;
                    _mergeResultFeatureIndex = -1;

                    _mergeFeaturesWindow.ShowDialog();
                }

                if (_mergeResultFeatureIndex != -1)
                {
                    _viewModelMain.ChangeCursor(Cursors.Wait, "Processing ...");
                    bool startTransaction = _viewModelMain.DataBase.Transaction != null;

                    if (startTransaction)
                        _viewModelMain.DataBase.BeginTransaction(true, IsolationLevel.ReadCommitted);

                    try
                    {
                        _viewModelMain.ViewModelUpdate.UpdateIncidModifiedColumns(_viewModelMain.IncidsSelectedMap.ElementAt(0));

                        List<List<SqlFilterCondition>> resultFeatureWhereClause =
                            ViewModelWindowMainHelpers.GisSelectionToWhereClause(
                            new HluDataSet.incid_mm_polygonsRow[] { selectTable[_mergeResultFeatureIndex] },
                                _viewModelMain.GisIDColumnOrdinals, ViewModelWindowMain.IncidPageSize, selectTable);

                        if (resultFeatureWhereClause.Count != 1)
                            throw new Exception("Error getting result feature from database.");

                        List<List<SqlFilterCondition>> mergeFeaturesWhereClause =
                            ViewModelWindowMainHelpers.GisSelectionToWhereClause(
                            selectTable.Where((r, index) => index != _mergeResultFeatureIndex).ToArray(),
                                _viewModelMain.GisIDColumnOrdinals, ViewModelWindowMain.IncidPageSize, selectTable);

                        // historyTable contains rows of features merged into result feature (i.e. no longer existing)
                        // and last row with data of result feature (remaining in GIS, lowest toid_fragment_id of merged features)
                        // this last row must be removed before writing history
                        // but is needed to update geometry fields in incid_mm_polygons
                        DataTable historyTable = _viewModelMain.GISApplication.MergeFeatures(newToidFragmentID,
                            resultFeatureWhereClause[0].Select(c => c.Clone()).ToList(), _viewModelMain.HistoryColumns);

                        if (historyTable == null)
                            throw new Exception("GIS merge operation failed.");

                        DataTable resultTable = historyTable.Clone();
                        DataRow resultRow = historyTable.AsEnumerable().FirstOrDefault(r =>
                            r.Field<string>(_viewModelMain.HluDataset.history.toid_fragment_idColumn.ColumnName) == newToidFragmentID);
                        if (resultRow == null) throw new Exception(String.Format(
                            "Failed to obtain geometry data of result feature from {0}.", _viewModelMain.GISApplication.ApplicationType));
                        resultTable.LoadDataRow(resultRow.ItemArray, true);
                        resultRow.Delete();
                        historyTable.AcceptChanges();

                        // synchronize DB shadow copy of GIS layer
                        MergeSynchronizeIncidMMPolygons(selectTable, resultTable, newToidFragmentID,
                            resultFeatureWhereClause[0], mergeFeaturesWhereClause);

                        // insert history rows (fixed values incid, toid, newToidFragmentID)
                        Dictionary<int, string> fixedValues = new Dictionary<int, string>();
                        fixedValues.Add(_viewModelMain.HluDataset.history.incidColumn.Ordinal, selectTable[0].incid);
                        fixedValues.Add(_viewModelMain.HluDataset.history.toidColumn.Ordinal, selectTable[0].toid);
                        fixedValues.Add(_viewModelMain.HluDataset.history.toid_fragment_idColumn.Ordinal, newToidFragmentID);
                        ViewModelWindowMainHistory vmHist = new ViewModelWindowMainHistory(_viewModelMain);
                        vmHist.HistoryWrite(fixedValues, historyTable, ViewModelWindowMain.Operations.PhysicalMerge);

                        if (startTransaction)
                        {
                            _viewModelMain.DataBase.CommitTransaction();
                            _viewModelMain.HluDataset.AcceptChanges();
                        }

                        // Re-count the incid records in the database.
                        _viewModelMain.IncidRowCount(true);

                        // Reset the incid and map selections but don't move
                        // to the first incid in the database.
                        _viewModelMain.ClearFilter(false);

                        // Synch with the GIS selection.
                        //---------------------------------------------------------------------
                        // FIX: 027 Force refill of Incid table after split/merge
                        // Force the Incid table to be refilled because it has been
                        // updated directly in the database rather than via the
                        // local copy.
                        _viewModelMain.RefillIncidTable = true;
                        //---------------------------------------------------------------------
                        _viewModelMain.ReadMapSelection(true);
                    }
                    catch
                    {
                        if (startTransaction) _viewModelMain.DataBase.RollbackTransaction();
                        throw;
                    }
                }
            }
            catch (Exception ex)
            {
                success = false;
                MessageBox.Show("Merge operation failed. The error message returned was:\n\n" +
                    ex.Message, "HLU Merge Error", MessageBoxButton.OK, MessageBoxImage.Error);
            }
            finally { _viewModelMain.ChangeCursor(Cursors.Arrow, null); }
            return success;
        }
        //---------------------------------------------------------------------
        //---------------------------------------------------------------------
        // CHANGED: CR39 (Split and merge complete messages)
        // Return true or false success so the main class knows
        // whether to notify the user following the completion of
        // the merge.
        //
        private bool PerformLogicalMerge(bool physicallyMerge)
        {
            bool success = true;
            try
            {
                if (_viewModelMain.IncidsSelectedMapCount <= 0)
                    return false;

                _mergeFeaturesWindow = new WindowMergeFeatures();
                _mergeFeaturesWindow.Owner = App.Current.MainWindow;
                _mergeFeaturesWindow.WindowStartupLocation = WindowStartupLocation.CenterOwner;
                _mergeFeaturesWindow.MaxHeight = App.Current.MainWindow.ActualHeight;

                HluDataSet.incidDataTable selectTable = new HluDataSet.incidDataTable();
                _viewModelMain.HluTableAdapterManager.incidTableAdapter.Fill(selectTable,
                    ViewModelWindowMainHelpers.IncidSelectionToWhereClause(ViewModelWindowMain.IncidPageSize,
                    _viewModelMain.IncidTable.incidColumn.Ordinal, _viewModelMain.IncidTable, _viewModelMain.IncidsSelectedMap));

                HluDataSet.incid_mm_polygonsDataTable polygons = new HluDataSet.incid_mm_polygonsDataTable();
                _viewModelMain.GetIncidMMPolygonRows(ViewModelWindowMainHelpers.GisSelectionToWhereClause(
                    _viewModelMain.GisSelection.Select(), _viewModelMain.GisIDColumnOrdinals,
                    ViewModelWindowMain.IncidPageSize, polygons), ref polygons);

                _mergeFeaturesViewModelLogical = new ViewModelMergeFeatures<HluDataSet.incidDataTable,
                    HluDataSet.incidRow>(selectTable, _viewModelMain.GisIDColumnOrdinals,
                    _viewModelMain.IncidTable.incidColumn.Ordinal, polygons.Select(r => r).ToArray(),
                    _viewModelMain.GISApplication);
                _mergeFeaturesViewModelLogical.DisplayName = "Select INCID To Keep";
                _mergeFeaturesViewModelLogical.RequestClose += new ViewModelMergeFeatures<HluDataSet.incidDataTable,
                        HluDataSet.incidRow>.RequestCloseEventHandler(_mergeFeaturesViewModelLogical_RequestClose);

                _mergeFeaturesWindow.DataContext = _mergeFeaturesViewModelLogical;
                _mergeResultFeatureIndex = -1;

                _mergeFeaturesWindow.ShowDialog();

                if (_mergeResultFeatureIndex == -1)
                    return false;

                _viewModelMain.ChangeCursor(Cursors.Wait, "Processing ...");

                _viewModelMain.DataBase.BeginTransaction(true, IsolationLevel.ReadCommitted);

                try
                {
                    string keepIncid = selectTable[_mergeResultFeatureIndex].incid;

                    // assign selected incid to selected features except keepIncid
                    DataTable historyTable = _viewModelMain.GISApplication.MergeFeaturesLogically(
                        keepIncid, _viewModelMain.HistoryColumns);

                    if ((historyTable == null) || (historyTable.Rows.Count == 0))
                        throw new Exception("Failed to update GIS layer.");

                    // assign selected incid and new toid_fragment_id to selected features except keepIncid in DB shadow copy
                    string toidFragmentFormat = String.Format("D{0}",
                        _viewModelMain.HluDataset.incid_mm_polygons.toid_fragment_idColumn.MaxLength);

                    List<KeyValuePair<int, object>> updateFields = new List<KeyValuePair<int,object>>();
                    var keepPolygon = polygons.FirstOrDefault(r => r.incid == keepIncid);
                    if (keepPolygon != null)
                    {
                        updateFields = (from c in polygons.Columns.Cast<DataColumn>()
                                        where (c.Ordinal != _viewModelMain.HluDataset.incid_mm_polygons.incidColumn.Ordinal) &&
                                            (c.Ordinal != _viewModelMain.HluDataset.incid_mm_polygons.toidColumn.Ordinal) &&
                                            (c.Ordinal != _viewModelMain.HluDataset.incid_mm_polygons.toid_fragment_idColumn.Ordinal) &&
                                            (c.Ordinal != _viewModelMain.HluDataset.incid_mm_polygons.shape_lengthColumn.Ordinal) &&
                                            (c.Ordinal != _viewModelMain.HluDataset.incid_mm_polygons.shape_areaColumn.Ordinal)
                                        select new KeyValuePair<int, object>(c.Ordinal, keepPolygon[c.Ordinal])).ToList();
                    }

                    var updatePolygons = from r in polygons
                                            where r.incid != keepIncid
                                            orderby r.toid, r.toid_fragment_id
                                            select r;

                    // update shadow DB copy of GIS layer
                    foreach (HluDataSet.incid_mm_polygonsRow r in updatePolygons)
                    {
                        r.incid = keepIncid;
                        for (int i = 0; i < updateFields.Count; i++)
                            r[updateFields[i].Key] = updateFields[i].Value;
                    }

                    if (_viewModelMain.HluTableAdapterManager.incid_mm_polygonsTableAdapter.Update(polygons) == -1)
                        throw new Exception(String.Format("Failed to update {0} table.", _viewModelMain.HluDataset.incid_mm_polygons.TableName));

                    // insert history rows (fixed value keepIncid)
                    Dictionary<int, string> fixedValues = new Dictionary<int, string>();
                    fixedValues.Add(_viewModelMain.HluDataset.history.incidColumn.Ordinal, keepIncid);
                    ViewModelWindowMainHistory vmHist = new ViewModelWindowMainHistory(_viewModelMain);
                    vmHist.HistoryWrite(fixedValues, historyTable, ViewModelWindowMain.Operations.LogicalMerge);

                    // count incid records no longer in use
                    List<string> deleteIncids = new List<string>();

                    IDataReader delReader = _viewModelMain.DataBase.ExecuteReader(String.Format(
                        "SELECT {0} FROM {1} WHERE {0} IN ({2}) GROUP BY {0} HAVING COUNT(*) = 0",
                        _viewModelMain.DataBase.QuoteIdentifier(_viewModelMain.IncidTable.incidColumn.ColumnName),
                        _viewModelMain.DataBase.QualifyTableName(_viewModelMain.IncidTable.TableName),
                        selectTable.Aggregate(new StringBuilder(), (sb, r) => sb.Append("," +
                            _viewModelMain.DataBase.QuoteValue(r.incid))).Remove(0, 1)),
                        _viewModelMain.DataBase.Connection.ConnectionTimeout, CommandType.Text);

                    if (delReader == null) throw new Exception("Error reading incid database table.");

                    while (delReader.Read())
                        deleteIncids.Add(delReader.GetString(0));
                    delReader.Close();

                    // delete any incid records no longer in use
                    if (deleteIncids.Count > 0)
                    {
                        int numAffected = _viewModelMain.DataBase.ExecuteNonQuery(String.Format(
                            "DELETE FROM {0} WHERE {1} IN ({2})",
                            _viewModelMain.DataBase.QualifyTableName(_viewModelMain.HluDataset.incid.TableName),
                            _viewModelMain.DataBase.QuoteValue(_viewModelMain.HluDataset.incid.incidColumn.ColumnName),
                            String.Join(",", deleteIncids.Select(i => _viewModelMain.DataBase.QuoteValue(i)).ToArray())),
                            _viewModelMain.DataBase.Connection.ConnectionTimeout, CommandType.Text);

                        if (numAffected > 0) _viewModelMain.IncidRowCount(true);
                    }

                    _viewModelMain.ViewModelUpdate.UpdateIncidModifiedColumns(keepIncid);

                    if (physicallyMerge && (MessageBox.Show("Perform physical merge as well?", "HLU: Physical Merge",
                        MessageBoxButton.YesNo, MessageBoxImage.Question, MessageBoxResult.No) == MessageBoxResult.Yes))
                    {
                        // restore the selection
                        _viewModelMain.GisSelection.Clear();
                        foreach (HluDataSet.incid_mm_polygonsRow r in polygons)
                        {
                            DataRow newRow = _viewModelMain.GisSelection.NewRow();
                            for (int i = 0; i < _viewModelMain.GisIDColumnOrdinals.Length; i++)
                                newRow[i] = r[_viewModelMain.GisIDColumnOrdinals[i]];
                            _viewModelMain.GisSelection.Rows.Add(newRow);
                        }

                        PerformPhysicalMerge();
                    }
                    else
                    {
                        _viewModelMain.DataBase.CommitTransaction();
                        _viewModelMain.HluDataset.AcceptChanges();

                        // Re-count the incid records in the database.
                        _viewModelMain.IncidRowCount(true);

                        // Reset the incid and map selections but don't move
                        // to the first incid in the database.
                        _viewModelMain.ClearFilter(false);

                        // Synch with the GIS selection.
                        //---------------------------------------------------------------------
                        // FIX: 027 Force refill of Incid table after split/merge
                        // Force the Incid table to be refilled because it has been
                        // updated directly in the database rather than via the
                        // local copy.
                        _viewModelMain.RefillIncidTable = true;
                        //---------------------------------------------------------------------
                        _viewModelMain.ReadMapSelection(true);
                    }
                }
                catch
                {
                    _viewModelMain.DataBase.RollbackTransaction();
                    throw;
                }
            }
            catch (Exception ex)
            {
                success = false;
                MessageBox.Show("Merge operation failed. The error message returned was:\n\n" +
                    ex.Message, "HLU Merge Error", MessageBoxButton.OK, MessageBoxImage.Error);
            }
            finally { _viewModelMain.ChangeCursor(Cursors.Arrow, null); }
            return success;
        }