Why can't access GetParentRow in one-to-one relationship

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C#

SQL-Server

SQL-Server-2008

Hi all fri,

here i have problem about data relation in ms sql.
i have 2 tables, A and B
A _ JobID (pk)
B _ JobID

i want to make one-to-one relation in dataset designer
Q1. how to set it? ( for me, 1-many is ok)

after i 1-1 relation in designer,

for (int i = 0; i < gridView1.SelectedRowsCount; i++)
            {
                if (gridView1.GetSelectedRows()[i] >= 0)
                    rows.Add(gridView1.GetDataRow(gridView1.GetSelectedRows()[i]));
                    
            }
            for (int j = 0; j < rows.Count; j++)
            {
                DataRow selectedRow = gridView1.GetFocusedDataRow();

                bRow= selectedRow as MyDataSet.BTableRow;
            
                DataRow parents = bRow.GetParentRow(dataRelation);               
                
            }

i have set dataRelation variable like this

string relation = "ATable_BTable";

DataRelation dataRelation = MyDataSet.BTable.ParentRelations[relation];

In designer, i set correct key column, foreign key column, parent table and child table.

But what's wrong in my code, i got null value in parents datarow although there are 1-1 mapping in DataTable(Database) .
I used the similar way in 1-many relation in other two tables that use the "ChildRelation" .
My tools visual studio 2010, ms sql , c#

Anyone wants to help me? I spent nearly one day :( so bad
thanks in advance