Why doesn't entity framework return any rows from related tables - entity-framework

Question

I wrote this code
class Student {
public Student() {
this.Courses = new HashSet<Course>();
}
public int ID { get; set; }
public string Name { get; set; }
public virtual ICollection<Course> Courses { get; set; }
}
class Course {
public Course() {
this.Students = new HashSet<Student>();
}
public int ID { get; set; }
public string Name { get; set; }
public virtual ICollection<Student> Students { get; set; }
}
class SchoolDBContext : DbContext {
public DbSet<Student> Students { get; set; }
public DbSet<Course> Courses { get; set; }
public SchoolDBContext()
: base("SchoolDbConnectionString") {
}
protected override void OnModelCreating(DbModelBuilder modelBuilder) {
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
}
}
My Seed method looks like
protected override void Seed(ConsoleApplication6.SchoolDBContext context)
{
Course c1 = new Course { ID = 1, Name = "Chemistry" };
Course c2 = new Course { ID = 2, Name = "Maths" };
Course[] courses = new Course[2];
courses[0] = c1;
courses[1] = c2;
Student s1 = new Student { ID = 1, Name = "Student 1" };
Student s2 = new Student { ID = 1, Name = "Student 2" };
Student[] students = new Student[2];
students[0] = s1;
students[1] = s2;
c1.Students = students;
c2.Students = students;
context.Courses.AddOrUpdate(course => new { course.ID }, courses);
}
After I run Update-database I can see that the database has 3 tables. Student and Course tables have 2 rows each and StudentCourse table has 4 rows. So I guess all data is seeded correctly.
Now when I write this code in my main method
static void Main(string[] args) {
SchoolDBContext c = new SchoolDBContext();
c.Configuration.LazyLoadingEnabled = true;
Student s = (from student in c.Students where student.ID == 1 select student).FirstOrDefault();
List<Course> courses = s.Courses.ToList();
Console.WriteLine(s.Name);
Console.WriteLine(courses.Count);
foreach (Course co in courses) {
Console.WriteLine(co.Name);
}
}
it prints the name of the student correctly... but prints 0 for courses.Count and the forloop on courses List returns nothing.
why am I not able to get the courses for student 1?
I also tried the other way round
static void Main(string[] args) {
SchoolDBContext c = new SchoolDBContext();
c.Configuration.LazyLoadingEnabled = true;
Course co = (from course in c.Courses where course.ID == 1 select course).FirstOrDefault();
Console.WriteLine(co.Name);
List<Student> students = co.Students.ToList();
foreach (Student s in students) {
Console.WriteLine(s.Name);
}
}
here also the name of the course is returned correctly... but it doesn't print any of the students.
So entity framework is not able to walk to the related table and fetch rows from there.
What's going on?

Answer 1

Found the answer myself.
static void Main(string[] args) {
SchoolDBContext c = new SchoolDBContext();
c.Configuration.LazyLoadingEnabled = false;
Course co = (from course in c.Courses.Include("Students") where course.ID == 1 select course).FirstOrDefault();
Console.WriteLine(co.Name);
List<Student> students = co.Students.ToList();
foreach (Student s in students) {
Console.WriteLine(s.Name);
}
}
putting it here so that it benefits someone....
But according to me my original code should have worked (lazy loading) so I don't understand why my original code which was doing lazy loading did not work.

Answer 2

OK. here is the solution with lazy loading
static void Main(string[] args) {
SchoolDBContext context = new SchoolDBContext();
context.Configuration.LazyLoadingEnabled = true;
Course co = (from course in context.Courses where course.ID == 1 select course).FirstOrDefault();
//Course co = (from course in c.Courses where course.ID == 1 select course).FirstOrDefault();
Console.WriteLine(co.Name);
foreach (Student s in context.Entry(co).Collection(c => c.Students).Query()) {
Console.WriteLine(s.Name);
}
}
This was really useful
http://msdn.microsoft.com/en-us/data/jj574232#lazy