Adding a collection, loop needed?

Question

Hello

I have this code:

Schedule s = _entities.Schedules.Where(x => x.ScheduleID == schedule.ScheduleID && x.BookingObject.BookingObjectID == bookingObjectID).FirstOrDefault();

if(s == null)
    s = new Schedule();

s.ScheduleStart = schedule.ScheduleStart;
s.ScheduleEnd = schedule.ScheduleEnd;

foreach (var t in schedule.Timetables)
{   
    s.Timetables.Add(t);
}

_entities.AddToSchedules(s);

_entities.SaveChanges();

Exception: System.InvalidOperationException

the object schedule gets passed in as a parameter

EDIT:

changed to:

  Schedule sh = new Schedule();


  sh.ScheduleStart = schedule.ScheduleStart;
  sh.ScheduleEnd = schedule.ScheduleEnd;

  foreach (var t in schedule.Timetables)
  {
       //sh.Timetables.Add(t);  // doesn't work
        sh.Timetables.Add(new Timetable { DayOfWeek = t.DayOfWeek, StartTime = t.StartTime, EndTime = t.EndTime });   // works
  }

  _entities.AddToSchedules(sh);

  _entities.SaveChanges();

is there some logical reason why sh.Timetables.Add(t) doesn't work since its a collection of Timetable?

/M

Answer 1

s.Timetables.Add(schedule.Timetables)

if this isn't the case, it's likely your question needs more information. What is s.Timetables, schedule.Timetables? (types)

Answer 2

foreach(var time in schedule.Timetables){
     s.Timetables.Add(time)
}

You can loop over the time tables in schedule.Timetables and add them to your new entity.

Answer 3

Another option would be:

((List<TimeTable>)s.Timetables).AddRange(((List<TimeTable>)schedule.Timetables));

Answer 4

Look at the first few lines:

Schedule s = _entities.Schedules.Where(x => x.ScheduleID == schedule.ScheduleID && x.BookingObject.BookingObjectID == bookingObjectID).FirstOrDefault();

if(s == null)
    s = new Schedule();

On the first line, you're querying the database for an object with the same ScheduleID as schedule and storing the returned reference in s. Assuming that object is available in the database, you're effectively pointing s at the same object as schedule. That means s.Timetables and schedule.Timetables are the same collection, which will cause the exception you're getting during the foreach.

I assume you only want to clone the object pointed to by schedule and insert it into the database if it is not already in the database. In that case:

Schedule s = _entities.Schedules.Where(x => x.ScheduleID == schedule.ScheduleID && x.BookingObject.BookingObjectID == bookingObjectID).FirstOrDefault();

if(s == null)
{
    s = new Schedule();

    s.ScheduleStart = schedule.ScheduleStart;
    s.ScheduleEnd = schedule.ScheduleEnd;

    foreach (var t in schedule.Timetables)
    {   
        s.Timetables.Add(t);
    }

    _entities.AddToSchedules(s);

    _entities.SaveChanges();
}

Answer 5

UPDATE: Just confirmed that this is likely to be the reason. And created a new tip in my tips series to explain.

I can think of one possible reason.

Is the relationship between schedule.Timetables one to many? I.e. a timetable can only be assigned to one schedule at a time?

If so this is failing:

  foreach (var t in schedule.Timetables)  {       
     sh.Timetables.Add(t); 
  }

Because as you add the 't' to a different schedule it is automatically removed from the old schedule.Timetables collection, which of course modifies the collection you are enumerating, which is a no-no.

if so the solution is simply to do something like this:

  var timetables = schedule.Timetables.ToArray();
  foreach (var t in timetables)  {       
     sh.Timetables.Add(t); 
  }

Here you enumerate the collection, before you start modifying it.

Is that it?

Alex