C#中如何使用EF Core的导航属性？如何配置关系？

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }

    // 导航属性：一个用户有多个订单
    public ICollection<Order> Orders { get; set; }
}

public class Order
{
    public int Id { get; set; }
    public DateTime OrderDate { get; set; }
    public int UserId { get; set; } // 外键

    // 导航属性：一个订单属于一个用户
    public User User { get; set; }
}

public class Order
{
    public int Id { get; set; }
    [ForeignKey("UserId")]
    public User User { get; set; }
    public int UserId { get; set; }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<User>()
        .HasMany(u => u.Orders)
        .WithOne(o => o.User)
        .HasForeignKey(o => o.UserId);
}

modelBuilder.Entity<Author>()
    .HasMany(a => a.Books)
    .WithOne(b => b.Author)
    .HasForeignKey(b => b.AuthorId);

modelBuilder.Entity<Person>()
    .HasOne(p => p.Passport)
    .WithOne(p => p.Person)
    .HasForeignKey<Passport>(p => p.PersonId);

public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection<Course> Courses { get; set; }
}

public class Course
{
    public int Id { get; set; }
    public string Title { get; set; }
    public ICollection<Student> Students { get; set; }
}

modelBuilder.Entity<Student>()
    .HasMany(s => s.Courses)
    .WithMany(c => c.Students);

// 查询用户及其所有订单
var usersWithOrders = context.Users
    .Include(u => u.Orders)
    .ToList();

context.Users
    .Include(u => u.Orders)
        .ThenInclude(o => o.OrderItems)
    .ToList();