Seed the Database with Test Data

I was wondering if I could get an explanation of the few line bellow from this code that I found from this tutorial...http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/creating-a-more-complex-data-model-for-an-asp-net-mvc-application

students.ForEach(s => context.Students.AddOrUpdate(p => p.LastName, s));

Explantion?
--------------------------

  var courses = new List<Course>
            {
                new Course {CourseID = 1050, Title = "Chemistry",      Credits = 3,
                  DepartmentID = departments.Single( s => s.Name == "Engineering").DepartmentID,
                  Instructors = new List<Instructor>()
                },


Explantion?
--------------------------



    AddOrUpdateInstructor(context, "Chemistry", "Kapoor");
            AddOrUpdateInstructor(context, "Chemistry", "Harui");


  StudentID = students.Single(s => s.LastName == "Barzdukas").ID,
                    CourseID = courses.Single(c => c.Title == "Chemistry").CourseID,
                    Grade = Grade.B  



Explantion?
--------------------------
foreach (Enrollment e in enrollments)
            {
                var enrollmentInDataBase = context.Enrollments.Where(
                    s =>
                         s.Student.ID == e.StudentID &&
                         s.Course.CourseID == e.CourseID).SingleOrDefault();
                if (enrollmentInDataBase == null)
                {
                    context.Enrollments.Add(e);
                }
            }
            context.SaveChanges();
        }

        void AddOrUpdateInstructor(SchoolContext context, string courseTitle, string instructorName)
        {
            var crs = context.Courses.SingleOrDefault(c => c.Title == courseTitle);
            var inst = crs.Instructors.SingleOrDefault(i => i.LastName == instructorName);
            if (inst == null)
                crs.Instructors.Add(context.Instructors.Single(i => i.LastName == instructorName));
        }
    }



Explantion?
--------------------------
yguyon28Asked:
Who is Participating?
 
QuinnDexCommented:
works in context with other fields, if it exists already then performs update else adds a new record.
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QuinnDexCommented:
the tutorial explains this code and what it is doing, and why you have created an empty list for Instructors.

Read it again go through the code, come back with more specific questions on what you dont understand.
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yguyon28Author Commented:
I'm not really sure how to understand the sentence bellow....
          students.ForEach(s => context.Students.AddOrUpdate(p => p.LastName, s));
0
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