C＃實體框架 - 社交網絡 - 友誼，聊天實體

Question

我想爲我的社交網絡學校項目做一個數據庫模型。我正在使用實體框架6.問題是我應該如何建模我的Friendship和Chat實體。

我得到這個錯誤：

Unhandled Exception:
System.Data.Entity.ModelConfiguration.ModelValidationException: One or more validation errors were detected during model generation:

Friendship_Chat_Source: : Multiplicity is not valid in Role 'Friendship_Chat_Source' in relationship 'Friendship_Chat'. Because the dependent role properties are not the key properties, the upper bound of the multiplicity of the dependent role must be '*'.

它有可能是一些與此有關：EF Code-First One-to-one relationship: Multiplicity is not valid in Role * in relationship

我真的不明白我應該怎麼辦在這裏。即使我以某種方式擺脫了這個錯誤（不同的數據庫模型），友誼表中的實體框架創建User_Id列作爲外鍵，我真的不知道它爲什麼會這樣做（我不希望它在那裏）。但我真的覺得我的模型應該看起來像這樣，沒有什麼不同。所以我想弄清楚，我該如何編輯這個模型。但是，如果你有不同的模型想法，我也會很感激。

用戶實體：

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

    [Required, MinLength(1), MaxLength(50)] 
    public string NickName { get; set; } 

    [Required, MinLength(6), MaxLength(50)] 
    public string PasswordHash { get; set; } 

    #region Settings 

    //true if anyone can see user posts 
    public Visibility PostVisibilityPreference { get; set; } = Visibility.Visible; 

    #endregion 

    #region Navigation properties 

    public virtual HashSet<Friendship> Friendships { get; set; } 
    public virtual HashSet<Post> Posts { get; set; } 
    public virtual HashSet<GroupUser> GroupUsers { get; set; } 
    public virtual HashSet<Comment> Comments { get; set; } 

    #endregion 
} 

友誼實體：

public class Friendship 
{ 
    #region Primary keys 

    public int User1Id { get; set; } 
    public int User2Id { get; set; } 

    #endregion 

    [Required] 
    public DateTime FriendshipStart { get; set; } 

    #region Foreign keys 

    //defined using fluent api in MyDbContext: 
    //User1Id 
    //User2Id 
    //and 

    [ForeignKey("Chat")] 
    public int? ChatId { get; set; } 

    #endregion 

    #region Navigation properties 

    public virtual User User1 { get; set; } 
    public virtual User User2 { get; set; } 
    public virtual Chat Chat { get; set; } 

    #endregion 
} 

隨着MyDbContext這個overrided功能OnModelCreating：

protected override void OnModelCreating(DbModelBuilder builder) 
    { 
     builder.Entity<Friendship>() 
      .HasKey(k => new { k.User1Id, k.User2Id }); 

     builder.Entity<Friendship>() 
      .HasRequired(u => u.User1) 
      .WithMany() 
      .HasForeignKey(u => u.User1Id); 

     builder.Entity<Friendship>() 
      .HasRequired(u => u.User2) 
      .WithMany() 
      .HasForeignKey(u => u.User2Id) 
      .WillCascadeOnDelete(false); 
    } 

聊天實體：

public class Chat 
{ 
    public int Id { get; set; } 

    #region Foreign keys 

    public int? FriendshipUser1Id { get; set; } 
    public int? FriendshipUser2Id { get; set; } 

    #endregion 

    #region Navigation properties 

    public virtual HashSet<Message> Messagges { get; set; } 

    [ForeignKey("FriendshipUser1Id, FriendshipUser2Id")] 
    public virtual Friendship Friendship { get; set; } 

    #endregion 
} 

Answer 1

如果我理解你的模型是正確的。 1友誼有1個user1和1個user2。您的設置被排除在外。

builder.Entity<Friendship>() 
     .HasRequired(u => u.User1) 
     .WithMany() 
     .HasForeignKey(u => u.User1Id); 

這意味着user1有很多......（很多是什麼？）。模型沒有任何可以接受這些設置的列表。你的模型只有單個對象。

如果你想要一對一/零：

builder.Entity<Friendship>() 
     .HasRequired(u => u.User1) 
     .WithRequiredDependant(u => u.User2) 
     or 
     .WithRequiredPrincipal(u => u.User2) 
     or 
     .WithOptional(u => u.User2) 

您也可以嘗試，例如複合鍵：Creating Composite Key Entity Framework

此外，我建議你使用或流利的API或數據註解慣例。它會使你的代碼更具可讀性。