Do all associated objects have to be accessed (lazyloaded) before an existing object can be saved?

Question

I'm learning EF Code First and am having trouble when updating existing records. I've boiled it down to this simple example:

This works:

using(var db = new DataContext()){
   var p = db.People.Find(1);
   p.Name="New Name";
   Console.WriteLine(p.Gender.Name); //<--Unnecessary property access
   db.SaveChanges(); //Success
}

...but this fails (when the WriteLine is removed):

using(var db = new DataContext()){
   var p = db.People.Find(1);
   p.Name="New Name";
   db.SaveChanges(); //DbValidationError "Gender field is required."
}

Why do I have to access/load the Gender propery if I'm not using it and the data is already correctly stored in the database? I just want to change the Name on an existing record. In this example, Gender is a one-to-many association stored as Gender_Id in the People table. The classes are defined like this:

public class Person
{
    [Key]
    public int PersonId { get; set; }

    [Required, MaxLength(50)]
    public string Name { get; set; }

    [Required, Column("Gender")]
    virtual public GenderCode Gender { get; set; }
}

public class GenderCode
{
    [Key]
    public int Id { get; set; }

    [Required, MaxLength(10)]
    public string Name { get; set; }
}

public class DataContext:DbContext
{
    public DbSet<Person> People { get; set; }
    public DbSet<GenderCode> GenderCodes { get; set; }
}

Of course, the fully defined classes are to have many more fields. I'd rather not have to access every dependant property every time I want to modify an unrelated value.

Is there a way to load an object, change a field, and save it without loading all related objects first?

Answer 1

Yes, this is necessary because of some horrible design mistakes in EF.

Check out my similar question, EF: Validation failing on update when using lazy-loaded, required properties

One trick is declaring FK properties along with the OO relations:

[ForeignKey("GenderId"), Column("Gender")]
virtual public GenderCode Gender { get; set; }
[Required]
public int GenderId { get; set; }

Answer 2

It is because you are using data annotations and Required attribute has also meaning for validation. Once you set navigation property as Required by data annotation it must be filled / loaded when you are going to persist entity to the database.