GetChanges from merged datatables returns null

Question

I have following code:

DataTable datTable3 = new DataTable();
datTable3 = datTable1.Clone();

datTable2.Merge(datTable1);
datTable3 = datTable2.GetChanges();

Want I want to do is: Compare DataTable1 with DataTable2 and when there are rows in DataTable1 which aren't in DataTable 2 then add these rows into a new DataTable(3). This code above gives me an empty DataTable3 each time although the rows in the first dt are not equal to the rows in my second dt. what am I doing wrong? Sorry if that question may be too easy but I'm using C# since a couple of months.

EDIT: I found this solution which doesn't work for me... Why?

 DataTable datTable3 = new DataTable();
        datTable3 = datTable1.Clone();

        foreach (DataRow row in datTable1.Rows)
        {
            datTable3.ImportRow(row);
        }

        foreach (DataRow row in datTable3.Rows)
        {
            row.SetAdded();
        }

        datTable2.Merge(datTable3);
        DataTable datTableFinal = datTable2.GetChanges(DataRowState.Added); 
 // shows me a datatable with again the values from datTable1 
 // even if they are already in datTable2!
        datTable2.RejectChanges();
        datTable1.RejectChanges();

Answer 1

The DataTable.GetChanges() method Gets a copy of the DataTable that contains all changes made to it since it was loaded or AcceptChanges was last called.

In other words, GetChanges() is dependent on the DataRow.RowState property. A DataTable.Merge() will either preserve their 'RowState' property, or reset it to 'Unchanged'.

This means that when you merge two DataTables with rows that have 'Unchanged' RowStates, the merged table will also contain 'Unchanged' rows and the DataTable.GetChanges method will return null or Nothing.

EDIT : You can always iterate through the DataTable to see what rows are added to the merged table. Something like

foreach(DataRow row in datTable2.Rows)
{
     Console.WriteLine("--- Row ---"); // Print separator.
    foreach (var item in row.ItemArray) // Loop over the items.
    {
    Console.Write("Item: "); // Print label.
    Console.WriteLine(item); // Invokes ToString abstract method.
    }
}

Answer 2

Iterate through and use LoadDataRow(object[] value, bool fAcceptChanges) :

foreach (DataRow row in MergeTable.Rows)
{
    TargetTable.LoadDataRow(row.ItemArray, false);
}
var changes = TargetTable.GetChanges();

changes had the desired value when I tried this method.