hi i tried foreign key constraint in the following code,but not working (i.e not throws error when i tried to delete a row which is used by some other table),pls tell me know what is the issue on the following code

try
{
int salesid = 2;


DataSet ds1 = new DataSet();

DataSet fakeDS = new DataSet();
DataTable dt = null;
fakeDS.ReadXml(@"product.xml");

dt = fakeDS.Tables[0].Copy();
dt.TableName = "product";
ds1.Tables.Add(dt);

DataSet fakeDS2 = new DataSet();
DataTable dt2 = null;

fakeDS2.ReadXml(@"sales.xml");

dt2 = fakeDS2.Tables[0].Copy();
dt2.TableName = "sales";
ds1.Tables.Add(dt2);

DataColumn dcParent, dcChild;

dcChild = ds1.Tables["sales"].Columns["productid"];
dcParent = ds1.Tables["product"].Columns["id"];

ForeignKeyConstraint FKC = new ForeignKeyConstraint("foreignkeys", ds1.Tables["product"].Columns["id"], ds1.Tables["sales"].Columns["productid"]);
FKC.DeleteRule = Rule.None;
ds1.Tables[1].Constraints.Add(FKC);
ds1.Tables[1].AcceptChanges();
ds1.AcceptChanges();


for (int i = 0; i < ds1.Tables[1].Rows.Count; i++)
{
if (ds1.Tables[1].Rows[i]["salesid"].Equals(salesid.ToString()))
//if (ds1.Rows[i]["productid"].Equals(salesid.ToString()))
{
//dt2.Rows[i].Delete();

ds1.Tables[1].Rows[i].Delete();
ds1.AcceptChanges();
}
}
}
catch (Exception ex1)
{
MessageBox.Show(ex1.Message.ToString());
}