public CourseGroup Build()
{
if (Lecture == null)
{
throw new InvalidOperationException("The lecture must be set first.");
}
ClassAcitivity lecture = Lecture.CreateClassActivity();
IEnumerable <ClassAcitivity> practicalClasses = BuildClassActivities(PracticalClasses);
IEnumerable <ClassAcitivity> labs = BuildClassActivities(Labs);
var group = new CourseGroup(lecture, practicalClasses, labs);
lecture.Group = group;
SetGroup(group, practicalClasses);
SetGroup(group, labs);
return(group);
}
