Question

According to http://msdn.microsoft.com/en-us/library/ms810291.aspx, you can’t change the ReadOnly attribute of an Expression based column in your DataTable. I need to figure out a way to Evaluation the Expression on a DataTable column, then set the .Expression = null, then allow the editing of that Column:

The following code does not work, because when you set the Expression == null, it resets the value in the DataTable to DBNull:

_persistedDataTable.Columns[currentDataColumn.ColumnName].Expression = null;
_persistedDataTable.Columns[currentDataColumn.ColumnName].ReadOnly = false;

My idea is that i copy the current DataTable to a new DataTable, row by row without preserving the schema, allowing me to edit the new DataTable values (whether or not they were derived by Expressions or not)… I am just not sure how to do this.

Answer 1

Here is how i did it:

String dateFilter = "IIF([data_type] = 'smalldatetime', 'true!', '')";
            String targetFilter = "[source_field]"; 

            DataTable tempDataTable = new DataTable();

            //create fields field
            DataColumn order = new DataColumn("order", Type.GetType("System.Int32"));
            tempDataTable.Columns.Add(order);
            order.AutoIncrement = true;
            order.AutoIncrementSeed = 1;
            order.ReadOnly = false;

            _sourceDataAdapter.Fill(tempDataTable);
            tempDataTable.Columns.Add(new DataColumn("date_format", Type.GetType("System.String"), dateFilter));
            tempDataTable.Columns.Add(new DataColumn("target_field", Type.GetType("System.String"), targetFilter));

            tempDataTable.BeginInit();
            tempDataTable.EndInit();

            _dataTable.Columns.Add(new DataColumn("order", Type.GetType("System.Int32")));
            _dataTable.Columns.Add(new DataColumn("local_field", Type.GetType("System.String")));
            _dataTable.Columns.Add(new DataColumn("length", Type.GetType("System.Int32")));
            _dataTable.Columns.Add(new DataColumn("data_type", Type.GetType("System.String")));
            _dataTable.Columns.Add(new DataColumn("decimals", Type.GetType("System.Int32")));

            _dataTable.Columns.Add(new DataColumn("date_format", Type.GetType("System.String")));
            _dataTable.Columns.Add(new DataColumn("target_field", Type.GetType("System.String")));

            using (DataTableReader reader = tempDataTable.CreateDataReader())
            {
                while(reader.Read())
                {
                    if (reader.HasRows)
                    {
                        _dataTable.Rows.Add(reader.GetValue(0), reader.GetValue(1), reader.GetValue(2), reader.GetValue(3), reader.GetValue(4), reader.GetValue(5), reader.GetValue(6));
                    }
                }
            }

        }