为什么我在EntityFramework的Code First模式下创建的导航属性值总为null？

[weixin_38080213]

菜鸟初学求教，这是在项目中抽取出来的代码
public class User
{
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public int UserId { get; set; }

public virtual int UserType { get; set; }
}

public class Person : User
{
public override int UserType
{
get
{
return 0;
}
set
{
base.UserType = 0;
}
}

public string PersonName { get; set; }

public ICollection<Sunny.Models.WorkExperience> WorkExperiences { get; set; }
}

public class WorkExperience
{
[Key]
public int ExperienceId { get; set; }

public int PersonId { get; set; }

public string Job { get; set; }

[ForeignKey("PersonId")]
public Person Person { get; set; }
}

public class UserConfiguration : EntityTypeConfiguration<User>
{
public UserConfiguration()
{
this.Map<User>(user => user.ToTable("User"));
this.Map<Person>(person => person.ToTable("Person"));
}
}

public class DbContext : System.Data.Entity.DbContext
{
public DbContext() : base("name=Model")
{
}

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Configurations.Add(new UserConfiguration());
modelBuilder.Conventions.Remove<Conventions.PluralizingTableNameConvention>();
base.OnModelCreating(modelBuilder);
}

public DbSet<User> Users { get; set; }
public DbSet<Person> Persons { get; set; }
public DbSet<WorkExperience> WorkExperiences { get; set; }
}

static void Main(string[] args)
{
DbContext context = new Models.DbContext();

Person person = new Models.Person();
person.UserId = 1;
person.PersonName = "Name";
context.Persons.Add(person);

WorkExperience experience = new Models.WorkExperience();
experience.PersonId = 1;
experience.Job = "Coder";
context.WorkExperiences.Add(experience);

context.SaveChanges();

context = new DbContext();
Console.Write(context.WorkExperiences.First().Person == null);
Console.Read();
}

以上代码Main方法的运行结果为显示true，也就是说导航属性WorkExperiences.Person属性的值总为null，但数据库里面已经插入数据，请问为什么没有加载导航属性的值？问题出在哪里？