问菜鸟EF4.3与MVC4的关系

EN

public class MyClass
{
    // [Key] - Don't actually need this attribute
    // EF Code First has a number of conventions.
    // Columns called "Id" are assumed to be the Key.
    public Guid Id {get; set; }

    // This reference creates an 'Independent Association'.  The Database
    // foreign key is created by convention and hidden away in the code.
    [Required]
    public virtual OtherClass OtherClass { get; set; }

    // This setup explicitly declares the foreign key property.
    // Again, by convention, EF assumes that "FooId" will be the key for
    // a reference to object "Foo"

    // This will still be required and a cascade-on-delete property
    // like above - an int? would make the association optional.
    public int OtherClass2Id { get; set; }

    // Leave the navigation property as this - no [Required]
    public virtual OtherClass2 { get; set; }
}

public class MyClass
{
    public int Id {get; set; }
    public string Name { get; set; }
    [Required]  // Note the required.  An optional won't have issues below.
    public virtual OtherClass OtherClass { get; set; }
}

var c = db.MyClasses.Find(1);
c.Name = "Bruce Wayne";

// Validation error on c.OtherClass.
// EF expects required associations to be loaded.
db.SaveChanges();  

public class MyClass
{
    public Guid Id {get; set; }
    public string Name { get; set; }

    public int OtherClassId { get; set }
    public virtual OtherClass OtherClass { get; set; }
}

var c = db.MyClasses.Find(1);

// Stepping through dubugger, here, c.OtherClassId = old id

c.OtherClass = somethingElse;

// c.OtherClassId = old id - Object and id not synced!

db.SaveChanges();               

// c.OtherClassId = new id, association persists correctly though.