public class Department
    {
        public Department( )
        {
            Persons = new HashSet<Person>();
        }
        [Key]
        public int  DepartmentId { get; set; }
        public string Name { get; set; }

        public ICollection<Person> Persons { get; set; }
    }

    public class Person
    {
        public Person( )
        {
            Department = new Department();
        }
        [Key]
        public int PersonId { get; set; }
        public string Name { get; set; }

        public int DepartmentId { get; set; }
        [ForeignKey("DepartmentId")]
        public virtual Department Department { get; set; }
    }

    public class AllContent:DbContext
    {
        public AllContent( ):base("testData")
        {
            Database.SetInitializer<AllContent>(null);
        }

        public DbSet<Person> Persons { get; set; }
        public DbSet<Department> Departments { get; set; }
    }

            using (var db = new AllContent())
            {
                Person person = new Person();
                person.Name = "小王";
                person.Department.Name = "行政";

                db.Persons.Add(person);
                db.SaveChanges();
            }

            using (AllContent db = new AllContent())
            {
                Person person = db.Persons.Include(p => p.Department).FirstOrDefault();
            }