//-------------------------------------------------------------------------------------------------------
private void button3_Click(object sender, EventArgs e)
{
if (this.listBoxRegitered.SelectedItem == null)
{
MessageBox.Show("Select Class you want to drop");
return;
}
string selectedClass = this.listBoxRegitered.SelectedItem.ToString();
int index = this.listBox1.SelectedIndex;
Student student = (Student)students[index];
int stid = student.STID;
string[] values = selectedClass.Split(' ');
int crn = Convert.ToInt32(values[3]);
int cid = -1;
using (var db = new CoursemoEntities())
{
//begin transaction
using (var trans = db.Database.BeginTransaction())
{
try
{
delay();
//check if registerd on this class for multi-user operation
var xyz = (from h in db.StudentClasses
join i in db.Classes
on h.CID equals i.CID
join s in db.Students
on h.STID equals s.STID
where i.CRN == crn && h.STID == stid
select h).Count();
Console.WriteLine("to jest drop x: {0}", xyz);
//if its not on the list throw exception and rollback transaction
if (xyz == 0)
{
throw new System.InvalidOperationException("Aready on the list rollback");
}
//search class by crn
var query = from a in db.Classes
where a.CRN == crn
select a;
//update current total -1 and get course id
foreach (var p in query)
{
p.CurrentTotal = p.CurrentTotal - 1;
cid = p.CID;
}
//find student in sthe classes registered and remove
var q = from c in db.StudentClasses
where c.CID == cid && c.STID == stid
select c;
foreach (var p in q)
{
db.StudentClasses.Remove(p);
}
//now find if someone on the wait list if so remove from waitlist
//and add to registered
var x = -1;
try
{
x = (from s in db.StudentWaitLists
where s.CID == cid
select s).Min(c => c.SCID);
}
catch (Exception ex)
{
Console.WriteLine(ex);
x = -1;
}
//if x =-1 no one on the wait list ignore and coninue
if (x == -1)
{
Console.WriteLine("wait list is empty ");
}
//else create new student and put on the list
else
{
var h = from s in db.StudentWaitLists
where s.SCID == x
select new
{
STID = s.STID,
CID = s.CID,
YEARS = s.YEARS
};
StudentClass studentClass = new StudentClass();
foreach (var i in h)
{
studentClass.YEARS = i.YEARS;
studentClass.CID = i.CID;
studentClass.STID = i.STID;
}
//remove from waitlist
var z = from a in db.StudentWaitLists
where a.SCID == x
select a;
foreach (var i in z)
{
db.StudentWaitLists.Remove(i);
}
//update classes curent enrolment
var o = from i in db.Classes
where i.CID == cid
select i;
foreach (var i in o)
{
i.CurrentTotal = i.CurrentTotal + 1;
}
db.StudentClasses.Add(studentClass);
}
db.SaveChanges();
trans.Commit();
}
catch (Exception ex)
{
trans.Rollback();
MessageBox.Show("Rollback");
Console.WriteLine(ex);
}
}
}
//try catch if seleted item is null
try
{
clearTXTboxes();
getStudentLists();
getWaitAndEnrolmentLists();
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
}
//-------------------------------------------------------------------------------------------------------
//register for a course using transaction if fail then will rollback
private void button2_Click(object sender, EventArgs e)
{
if (this.listBox1.SelectedItem == null)
{
MessageBox.Show("Select Student");
return;
}
if (this.listBoxAvailableCourses.SelectedItem == null)
{
MessageBox.Show("Select Class from available courses.");
return;
}
using (var db = new CoursemoEntities())
{
using (var trans = db.Database.BeginTransaction())
{
ArrayList regiteredClasses = new ArrayList();
ArrayList waitList = new ArrayList();
delay();
string selectedClass = this.listBoxAvailableCourses.SelectedItem.ToString();
int index = this.listBox1.SelectedIndex;
int i = this.listBoxAvailableCourses.SelectedIndex;
Student student = (Student)students[index];
Class myClass = (Class)classes[i];
StudentClass studentClass = new StudentClass();
studentClass.YEARS = myClass.Years;
studentClass.STID = student.STID;
studentClass.CID = myClass.CID;
StudentWaitList studentWaitList = new StudentWaitList();
studentWaitList.YEARS = myClass.Years;
studentWaitList.STID = student.STID;
studentWaitList.CID = myClass.CID;
string[] values = selectedClass.Split(' ');
int crn = Convert.ToInt32(values[3]);
var x = (from c in db.Classes
join s in db.StudentClasses
on c.CID equals s.CID
where c.CRN == crn && s.STID == student.STID
select c).Count();
var y = (from c in db.Classes
join s in db.StudentWaitLists
on c.CID equals s.CID
where c.CRN == crn && s.STID == student.STID
select c).Count();
Console.WriteLine("this is x: {0}", x);
Console.WriteLine("this is y: {0}", y);
try
{
//check is student is on the wait list or class registerd list
//if is on either one cancel transaction
if (x > 0 || y > 0)
{
MessageBox.Show("You are on the list");
throw new System.InvalidOperationException("Aready on the list rollback");
}
//update classes total curretn
var query = from a in db.Classes
where a.CID == studentClass.CID
select a;
foreach (var p in query)
{
//if current enrolled equals capacity put student on the wait list
if (p.CurrentTotal == p.Capcity)
{
db.StudentWaitLists.Add(studentWaitList);
}
//else put on the registered list and update db
else
{
p.CurrentTotal = p.CurrentTotal + 1;
db.StudentClasses.Add(studentClass);
}
}
db.SaveChanges();
db.Database.CurrentTransaction.Commit();
}
catch (Exception ex)
{
trans.Rollback();
MessageBox.Show("rollback");
Console.WriteLine(ex);
}
}
}
//update gui
getStudentLists();
getWaitAndEnrolmentLists();
selectCourse(this.listBoxAvailableCourses.Text);
}
