DataClasses1DataContext dc = new DataClasses1DataContext();

var Q = from p in dc.Customers where p.id > 4 select p;

foreach (var q in Q)

                q.totalpurchase = 100;

var Q2 = from p in dc.Customers where p.id < 4 select p;

foreach (var q in Q2)

                q.totalpurchase = 500;

            dc.SubmitChanges();

SqlTransaction tran = null;

try

            {

                tran = con.BeginTransaction(IsolationLevel.ReadUncommitted);

                dc.Transaction = tran;

var Q3 = from p in dc.Customers where p.id > 4 select p;

foreach (var q in Q3)

                    q.totalpurchase = 100;

var Q4 = from p in dc.Customers where p.id < 4 select p;

foreach (var q in Q4)

                    q.totalpurchase = 500;

                dc.SubmitChanges();

SqlCommand cmd = new SqlCommand(@"update Customers set totalpurchase=totalpurchase+0.10
                                                  where cname='Franek'", con,tran);

                cmd.ExecuteNonQuery();       

System.Threading.Thread.Sleep(20000);

SqlCommand cmd2 = new SqlCommand(@"update Customers set totalpurchase=totalpurchase-0.10
                                                  where cname='Janek'", con, tran);

                cmd2.ExecuteNonQuery();

                tran.Commit();

                textBox1.Text = "done";

            }

catch(Exception ex)

            {

                tran.Rollback();

                textBox1.Text = ex.Message;

            }

Transaction Isolation Levels

Transaction Deadlocks