Esempio n. 1
0
        //
        // Drop():
        //
        // If possible, function drops the student from the course.
        //
        // Return values:
        //  -1 - error
        //  0 - dropped, no waitlist
        //  1 - dropped, enrolled student from waitlist
        //  2 - not enrolled, dropped from waitlist
        //  3 - student was not either enrolled or waitlisted
        //
        private int Drop(int sid, int cid)
        {
            int retries = 0;

            // make sure parameters are valid
            if (sid < 0 || cid < 0)
            {
                return(-1);
            }

            using (var db = new CoursemoDataContext())
            {
                while (retries < 3)
                {
                    try
                    {
                        var txOptions = new TransactionOptions();
                        txOptions.IsolationLevel = System.Transactions.IsolationLevel.Serializable;

                        using (var transaction = new TransactionScope(TransactionScopeOption.Required,
                                                                      txOptions))
                        {
                            // student enrolled, drop course and enroll first student on waitlist
                            if (StudentEnrolled(sid, cid))
                            {
                                db.UnregisterStudent(sid, cid);
                                // candidate on waitlist exists
                                int sidFromWaitList = GetFirstStudentFromWaitlist(cid);

                                System.Threading.Thread.Sleep(_delay);

                                if (sidFromWaitList != 0)
                                {
                                    db.RegisterStudent(sidFromWaitList, cid);
                                    db.UnwaitlistStudent(sidFromWaitList, cid);
                                    db.SubmitChanges();
                                    transaction.Complete();
                                    return(1);
                                }
                                db.SubmitChanges();
                                transaction.Complete();
                                return(0);
                            }
                            // student not enrolled, but waitlisted, remove from waitlist
                            else if (StudentWaitlisted(sid, cid))
                            {
                                db.UnwaitlistStudent(sid, cid);
                                db.SubmitChanges();
                                transaction.Complete();
                                return(2);
                            }
                            else
                            {
                                return(3);
                            }
                        }
                    }
                    catch (SqlException exc)
                    {
                        // deadlock
                        if (exc.Number == 1205)
                        {
                            retries++;
                        }
                    }
                    catch (Exception e)
                    {
                        MessageBox.Show("Drop(): " + e.Message);
                        return(-1);
                    }
                } // while
            }

            return(-1);
        }
Esempio n. 2
0
        //
        // Enroll():
        //
        // If possible, function enrolls the student in the course.
        //
        // Return values:
        //  -1 - error
        //  0 - Student already enrolled
        //  1 - Student enrolled
        //  2 - Student already waitlisted
        //  3 - Student waitlisted
        //
        private int Enroll(int sid, int cid)
        {
            int retries = 0;

            // make sure parameters are valid
            if (sid < 0 || cid < 0)
            {
                return(-1);
            }

            using (var db = new CoursemoDataContext())
            {
                while (retries < 3)
                {
                    try
                    {
                        var txOptions = new TransactionOptions();
                        txOptions.IsolationLevel = System.Transactions.IsolationLevel.Serializable;

                        using (var transaction = new TransactionScope(TransactionScopeOption.Required,
                                                                      txOptions))
                        {
                            // check if student is already enrolled
                            if (StudentEnrolled(sid, cid))
                            {
                                return(0);
                            }

                            // class is full, add to waitlist
                            if (GetCourseCapacity(cid) - GetCurrentEnrollment(cid) < 1)
                            {
                                // check if student is not on waitlist alread
                                if (StudentWaitlisted(sid, cid))
                                {
                                    return(2);
                                }

                                db.WaitlistStudent(sid, cid);
                                db.SubmitChanges();
                                transaction.Complete();
                                return(3);
                            }
                            // enroll
                            else
                            {
                                System.Threading.Thread.Sleep(_delay);

                                db.RegisterStudent(sid, cid);
                                db.SubmitChanges();
                                transaction.Complete();
                                return(1);
                            }
                        }
                    }
                    catch (SqlException exc)
                    {
                        // deadlock
                        if (exc.Number == 1205)
                        {
                            retries++;
                        }
                    }
                    catch (Exception e)
                    {
                        MessageBox.Show("Enroll(): " + e.Message);
                        return(-1);
                    }
                } // while
            }

            return(-1);
        } // Enroll()