Question

假设在数据模型中存在多对多关系。如何设置它以便id的列表被急切加载并且导航属性是延迟加载的？

在一对一的关系中，我可以轻松地使用ForeignKey属性来链接id和导航属性，但我不确定是否有链接集合的方法。我怎样才能确保两者一致？

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

   public ICollection<User> FollwerIds { get; set; }
   public ICollection<User> FollwingIds { get; set; }
   public virtual ICollection<User> Followers { get; set; }
   public virtual ICollection<User> Following { get; set; }
}

public class UserContext: DbContext {
    public DbSet<User> Users { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder) {
        base.OnModelCreating(modelBuilder);

        modelBuiler.Entity<User>()
            .HasMany(u => u.Followers)
            .WithMany(u => u.Following)
            .Map(m => m.MapLeftKey("FollowingUserId")
                .MapRightKey("FollowerUserId")
                .ToTable("UserFollowUser")
            );
    }
}

我想让ASP.NET中的控制器始终返回带有两个User Ids数组的User对象。谢谢。

Answer 1

在多对多中你不需要这个：

   public partial class ProgressForm : Form
    {
        public ProgressForm()
        {
            InitializeComponent();
            this.TopMost = true;
        }

        public void SetProgress(int progress)
        {
            this.progressBar1.Value = progress;
            // Allow the form to be repainted
            Application.DoEvents();
        }
    } 


    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        ProgressForm progressForm = new ProgressForm();
        void Task2()
        {
            ShowProgress(0);
            for (int i = 0; i < 10; i++ )
            {
                System.Threading.Thread.Sleep(1000);
                ShowProgress(i * 10);
            }
            HideProgress();
        }


        void ShowProgress(int progress)
        {
            if (!progressForm.Visible)
                progressForm.Show();
            progressForm.SetProgress(progress);
        }

        void HideProgress()
        {
            progressForm.Hide();  // or Close, it depends from app logic
        }


        private void button1_Click(object sender, EventArgs e)
        {
            Task2();
        }
    }

Answer 2

要使多对多关系有效，您需要：

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

   public virtual ICollection<User> Followers { get; set; }
   public virtual ICollection<User> Following { get; set; }
}

public class UserContext: DbContext {
    public DbSet<User> Users { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder) {
        base.OnModelCreating(modelBuilder);

        modelBuiler.Entity<User>()
            .HasMany(u => u.Followers)
            .WithMany(u => u.Following)
            .Map(m => m.MapLeftKey("FollowingUserId")
                .MapRightKey("FollowerUserId")
                .ToTable("UserFollowUser")
            );
    }
}

我相信这会按你的意愿运作。

实体框架多对多关系导航属性和ID

2 个答案: