How to implement the class - Student relationship in c#?

Question

I want to implement a system, which represents a ClassRoom- Student relationship. I want to impose the constraint that Each ClassRoom can have any number of students, but one student can be at only one ClassRoom.

I have created two classes - ClassRoom and Student. I have created a list in the Class ClassRoom.How do I ensure that no one can inser the same student in two classRooms.

Answer 1

I hope it is on your experience level:

ClassRoom

public class ClassRoom
{
    private List<Student> students = new List<Student>();

    public bool Contains(Student student)
    {
        return this.students.Contains(student);
    }

    public void Add(Student student)
    {
        if (!Contains(student))
            this.students.Add(student);
        student.StudentClassRoom = this;
    }

    public void Remove(Student student)
    {
        // if this contains, remove it anyway...
        if(Contains(student))
            this.students.Remove(student);

        // but do not set ClassRoom of student if she/he does not sit in this.
        if (student.StudentClassRoom != this)
            return;

        student.StudentClassRoom = null;
    }
}

Student

public class Student
{
    private ClassRoom stdClsRoom;
    public ClassRoom StudentClassRoom
    {
        get { return this.stdClsRoom; }
        set
        {
            if (value == this.stdClsRoom) //from null to null; from same to same;
                return;                   //do nothing

            if (this.stdClsRoom != null)  //if it set from something
            {
                ClassRoom original = this.stdClsRoom;
                this.stdClsRoom = null;  // set field to null to avoid stackoverflow
                original.Remove(this);   // remove from original
            }

            this.stdClsRoom = value;    // set field

            if (value != null)          //if it set to something
                value.Add(this);        // add to new
        }
    }
}