Entity Framework 6 navigation collections are null instead of empty

Question

I\'m trying to write a relational database application using Entity Framework 6. I have classes analogous to:

public class Subject
{
    public int ID { get; set         


        

Answer 1

As the official documentation demonstrates, you should always initialize your collection navigation properties inside the entity constructor if you want to prevent a Null reference exception.

public Subject()
{
    Students = new HashSet<Student>(); // you may also use List<Student>, but HashSet will guarantee that you are not adding the same Student mistakenly twice
}

Entity framework will fill Students property (using a proxy) only if there is at least a student, else it will leave the property as is (null if you have not initialized it).

When the entity is not a proxy, then Entity Framework tracks its changes only when calling SaveChanges() on the context, using its original entity state for comparison. This answer will further clarify this behavior.