//
// Swap():
//
// If possible, function swaps the courses for two student.
// So, if student s1 was enrolled in course c1, and student s2
// was enrolled in course c2, after succesful execution
// student s1 is enrolled in s2, and student s2 is enrolled in s1.
//
// Return values:
// 0 - failure
// 1 - success
//
private int Swap(int s1, int s2, int c1, int c2)
{
int retries = 0;
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))
{
// both students must be enrolled
if (StudentEnrolled(s1, c1) && StudentEnrolled(s2, c2))
{
db.UnregisterStudent(s1, c1);
db.RegisterStudent(s2, c1);
System.Threading.Thread.Sleep(_delay);
db.UnregisterStudent(s2, c2);
db.RegisterStudent(s1, c2);
db.SubmitChanges();
transaction.Complete();
return(1);
}
else
{
return(0);
}
}
}
catch (SqlException exc)
{
// deadlock
if (exc.Number == 1205)
{
retries++;
}
}
catch (Exception e)
{
MessageBox.Show("Swap(): " + e.Message);
return(0);
}
} // while
}
return(0);
} // Swap()
//
// ResetDatabase():
//
// Revert database to its inintial state.
// Deletes data from Registration and Waitlist tables.
//
private void ResetDatabase()
{
using (var db = new CoursemoDataContext())
{
try
{
var query1 = from r in db.Registrations select r;
db.Registrations.DeleteAllOnSubmit(query1);
var query2 = from w in db.Waitlists select w;
db.Waitlists.DeleteAllOnSubmit(query2);
db.SubmitChanges();
UpdateUi();
}
catch (Exception exc)
{
MessageBox.Show("ResetDatabase(): " + exc.Message);
}
}
}
//Delete all rows in Registrations, Transactions, and Waitlist tables
private void resetButton_Click(object sender, EventArgs e)
{
using (var db = new CoursemoDataContext())
{
var TxOptions = new System.Transactions.TransactionOptions();
TxOptions.IsolationLevel = System.Transactions.IsolationLevel.Serializable;
using (var Tx = new System.Transactions.TransactionScope(
System.Transactions.TransactionScopeOption.Required, TxOptions))
{
try
{
if (delay_flag)
{
Delay();
}
db.Registrations.DeleteAllOnSubmit(from r in db.Registrations select r);
if (delay_flag)
{
Delay();
}
db.Waitlists.DeleteAllOnSubmit(from w in db.Waitlists select w);
if (delay_flag)
{
Delay();
}
db.Transactions.DeleteAllOnSubmit(from t in db.Transactions select t);
db.SubmitChanges();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
finally
{
Tx.Complete();
}
}
MessageBox.Show("Database reset.");
}
}
//
// 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);
} // Drop()
//
// 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()
private void swapButton_Click(object sender, EventArgs e)
{
string netidA = this.netidATextBox.Text;
if (netidA == null)
{
MessageBox.Show("Enter student A's netid.");
return;
}
int crnA = Convert.ToInt32(this.crnATextBox.Text);
if (this.crnATextBox.Text == null)
{
MessageBox.Show("Enter student A's CRN.");
return;
}
string netidB = this.netidBTextBox.Text;
if (netidB == null)
{
MessageBox.Show("Enter student B's netid.");
return;
}
int crnB = Convert.ToInt32(this.crnBTextBox.Text);
if (this.crnBTextBox.Text == null)
{
MessageBox.Show("Enter student B's CRN.");
return;
}
string msg = null;
using (var db = new CoursemoDataContext())
{
var TxOptions = new System.Transactions.TransactionOptions();
TxOptions.IsolationLevel = System.Transactions.IsolationLevel.Serializable;
using (var Tx = new System.Transactions.TransactionScope(
System.Transactions.TransactionScopeOption.Required, TxOptions))
{
try
{
//Check if student A exists
if (delay_flag)
{
Delay();
}
var aExists = from s in db.Students
where s.Netid == netidA
select s.Netid;
if (!aExists.Any())
{
msg = netidA + " does not exist.";
throw new System.InvalidOperationException(msg);
}
//Check if student A is enrolled in crnA
var aEnrolled = from r in db.Registrations
where r.Netid == netidA
where r.CRN == crnA
select r;
if (!aEnrolled.Any())
{
msg = netidA + " is not enrolled in " + crnA.ToString() + ".";
throw new System.InvalidOperationException(msg);
}
if (delay_flag)
{
Delay();
}
//Check if student B exists
var bExists = from s in db.Students
where s.Netid == netidB
select s.Netid;
if (!bExists.Any())
{
msg = netidB + " does not exist.";
throw new System.InvalidOperationException(msg);
}
if (delay_flag)
{
Delay();
}
//Check if student B is enrolled in crnB
var bEnrolled = from r in db.Registrations
where r.Netid == netidB
where r.CRN == crnB
select r;
if (!bEnrolled.Any())
{
msg = netidB + " is not enrolled in " + crnB.ToString() + ".";
throw new System.InvalidOperationException(msg);
}
if (delay_flag)
{
Delay();
}
//Clear out student a's waitlist entry for b's class
var aWaiting = from w in db.Waitlists
where w.Netid == netidA
where w.CRN == crnB
select w;
db.Waitlists.DeleteAllOnSubmit(aWaiting);
if (delay_flag)
{
Delay();
}
//Clear out student b's waitlist entry for a's class
var bWaiting = from w in db.Waitlists
where w.Netid == netidB
where w.CRN == crnA
select w;
db.Waitlists.DeleteAllOnSubmit(bWaiting);
//Swap registrations
if (delay_flag)
{
Delay();
}
aEnrolled.First().CRN = crnB;
if (delay_flag)
{
Delay();
}
bEnrolled.First().CRN = crnA;
//MessageBox.Show(netidA + " swapped course " + crnA.ToString() + " for " + crnB.ToString() + " with " + netidB);
msg = netidA + " swapped course " + crnA.ToString() + " for " + crnB.ToString() + " with " + netidB;
db.SubmitChanges();
Tx.Complete();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
MessageBox.Show(msg);
}
//Get selected student and enrolled course
//Delete entry in registrations table
//Check waitlist for dropped course, enroll first in line
private void dropCourseButton_Click(object sender, EventArgs e)
{
Student student = getSelectedStudent();
if (student == null)
{
MessageBox.Show("Select a student.");
return;
}
if (this.registrationLB.SelectedItem == null)
{
MessageBox.Show("Select a registered course.");
return;
}
int selectedCRN = Convert.ToInt32(this.registrationLB.SelectedItem.ToString().Split(' ')[0]);
//MessageBox.Show(selectedCRN.ToString());
string msg = null;
using (var db = new CoursemoDataContext())
{
var TxOptions = new System.Transactions.TransactionOptions();
TxOptions.IsolationLevel = System.Transactions.IsolationLevel.Serializable;
using (var Tx = new System.Transactions.TransactionScope(
System.Transactions.TransactionScopeOption.Required, TxOptions))
{
try
{
if (delay_flag)
{
Delay();
}
db.Registrations.DeleteAllOnSubmit(from r in db.Registrations
where r.CRN == selectedCRN
where r.Netid == student.netid
select r);
//MessageBox.Show(student.netid + " dropped " + selectedCRN);
msg = student.netid + " dropped " + selectedCRN;
if (delay_flag)
{
Delay();
}
var waiting = (from w in db.Waitlists
where w.CRN == selectedCRN
orderby w.RegTime
select w).ToList();
//Is there a waitlist for this class?
if (waiting.Any())
{
if (delay_flag)
{
Delay();
}
var front = students.Find(
delegate(Student s)
{
return(s.netid == waiting[0].Netid);
}
);
//Enroll
if (delay_flag)
{
Delay();
}
Registration r = new Registration
{
Netid = front.netid,
CRN = selectedCRN
};
db.Registrations.InsertOnSubmit(r);
//MessageBox.Show(front.netid + " enrolled in " + selectedCRN);
//msg = front.netid + " enrolled in " + selectedCRN;
//Remove enrolled student from waitlist
if (delay_flag)
{
Delay();
}
db.Waitlists.DeleteAllOnSubmit(from w in db.Waitlists
where w.Netid == front.netid
where w.CRN == selectedCRN
select w);
}
db.SubmitChanges();
Tx.Complete();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
MessageBox.Show(msg);
}
//Get the selected student and course
//Try to enroll the student in the course
//If the course is full, put students on waitlist
private void enrollButton_Click(object sender, EventArgs e)
{
if (this.studentsLB.SelectedItem == null)
{
MessageBox.Show("Select a student to enroll.");
return;
}
Student student = getSelectedStudent();
//MessageBox.Show(student.ToString());
if (this.coursesLB.SelectedItem == null)
{
MessageBox.Show("Select a course to enroll in.");
return;
}
Course course = getSelectedCourse();
//MessageBox.Show(course.ToString());
string msg = null;
using (var db = new CoursemoDataContext())
{
var TxOptions = new System.Transactions.TransactionOptions();
TxOptions.IsolationLevel = System.Transactions.IsolationLevel.Serializable;
using (var Tx = new System.Transactions.TransactionScope(
System.Transactions.TransactionScopeOption.Required, TxOptions))
{
try {
if (delay_flag)
{
Delay();
}
var enrolled = from r in db.Registrations
where r.Netid == student.netid
where r.CRN == course.crn
select r;
if (delay_flag)
{
Delay();
}
var waiting = from w in db.Waitlists
where w.Netid == student.netid
where w.CRN == course.crn
select w;
//Is the student already enrolled in this class?
if (enrolled.Any())
{
//MessageBox.Show(student.netid + " is already enrolled in course " + course.crn);
msg = student.netid + " is already enrolled in course " + course.crn;
}
//Is the student on the waitlist for this class?
else if (waiting.Any())
{
//MessageBox.Show(student.netid + " is already on the waitlist for course " + course.crn);
msg = student.netid + " is already on the waitlist for course " + course.crn;
}
//Student not enrolled or waiting for this course
else
{
//Get number of registrations for this course
if (delay_flag)
{
Delay();
}
var query = (from r in db.Registrations
where r.CRN == course.crn
select r.RID).ToList();
//Is this class full?
if (query.Count == course.capacity)
{
//MessageBox.Show(course.crn + " is full, putting " + student.netid + " on the waitlist for this course.");
//Put on waitlist
if (delay_flag)
{
Delay();
}
Waitlist wait = new Waitlist
{
Netid = student.netid,
CRN = course.crn,
RegTime = DateTime.Now
};
db.Waitlists.InsertOnSubmit(wait);
if (delay_flag)
{
Delay();
}
var placeInLine = from w in db.Waitlists
where w.CRN == course.crn
orderby w.RegTime
select w.WID;
//MessageBox.Show(student.netid + " put on waitlist for " + course.crn + ". Place in line: " + (placeInLine.Count() + 1).ToString());
msg = student.netid + " put on waitlist for " + course.crn + ". Place in line: " + (placeInLine.Count() + 1).ToString();
}
else
{
//Enroll
if (delay_flag)
{
Delay();
}
Registration r = new Registration
{
Netid = student.netid,
CRN = course.crn
};
db.Registrations.InsertOnSubmit(r);
//MessageBox.Show(student.netid + " enrolled in " + course.crn);
msg = student.netid + " enrolled in " + course.crn;
}
}
db.SubmitChanges();
Tx.Complete();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
//msg = "Enrollment failed. Try again.";
//Tx.Dispose();
}
}
MessageBox.Show(msg);
}
}