Entity Framework 4, inserting with foreign key value not ID

Question

This is pretty basic question I am sure but it's baffling me now :S

I have 2 tables, Students and Courses with a foreign key constraint, Many Students to 1 Course.

I store in my Students table a CourseId_FK reference, so when I am creating a Student how would I be able to do something like this?

Students student = new Students();
student.Name = Bob;
student.Course.CourseName = "Geography";
db.SaveChanges();

Right now, the above doesn't work and I have to resolve to

student.CourseId = 22;

Can anyone help me pls?

Thanks

David

Tybalt

I'm a little confused, because student=> course is 1 to many, so should it be student.Courses? – Sclerotomy

@Vimvq1987 yes I am sorry, I made a mistake in my initial writing of my post, I have since corrected it, Many students to 1 course. – Tybalt

Answer 1

If you don't want to load the full course entity:

Student student = new Student();
student.Name = Bob;
student.CourseId = db.Courses
                     .Where(c => c.CourseName == "Geography")
                     .Select(c => c.CourseId).First();
db.SaveChanges();

This would only fetch the Id of the Geography course from DB (or crash when there isn't any).

Adriaadriaens

Thank you, this was what I was looking. The other answers opened my eyes though as well. Thank you all – Tybalt

Answer 2

Looking at your entities, does "Student" have a "Course" (Really: Courses) property?

Your entity should probably look something like this, for what you want to do:

public class Student
{
    public string Name {get; set;}

    public virtual ICollection<Course> Courses {get; set;}
}

Then you'd do something like:

Student student = new Student();
student.Name = Bob;
student.Courses.Add(db.Courses.Where(c => c.CourseName == "Geography"));

Edit: If the Student can only have one course, you modify the Student class so it looks like this:

public class Student
{
    public int StudentId {get; set;}
    public string Name {get; set;}
    public int CourseId {get; set;}
    public virtual Course Course {get; set;}
}

Then your code looks like this:

student.Course = db.Courses.Where(c => c.CourseName == "Geography"));

What's going on with your code (I expect) is that you only have the CourseId so when you're so you can't assign an actual course object to your student.

Negligible

Yes I apologies, 1 student can have only 1 course, I made a mistake when I was writing the original question. – Tybalt

Thank you, this one opened my eyes to make me understand more about Entity Framework, thank you – Tybalt

Answer 3

I'd do something like this:

Student student = new Student();
student.Name = Bob;
student.Course = db.Courses.First(c => c.CourseName == "Geography");
db.SaveChanges();

Update: the answer is about the situation when a student has zero or one course (as in the provided code).

Chaffin