如何在實體中設置兩個字段之間的一個方向關係（在同一個表中或不同的實體）

Question

我正在使用CodeFirst作爲我的開發。對於我的實體中的所有模型類，我有一個名爲CommonFields的基類

public class CommonFields 
{ 
    public int Status { get; set; } 
    public DateTime CreatedOn { get; set; } 
    public int CreaedBy { get; set; } 
    public DateTime ModifiedOn { get; set; } 
    public int ModifiedBy { get; set; } 
} 

而且，例如，我有兩個類，如

public class Employee : CommonFields 
{ 
    public int Id { get; set; } 
    public string Name { get; set; } 
    //Other properties 
} 

public class User : CommonFields 
{ 
    public int Id { get; set; } 
    public string Name { get; set; } 
    //Other properties 
} 

如何設置對應關係從CreatedBy & ModifiedBy到用戶表。我只需要一個方向映射。

我需要獲取用戶信息，當我寫objEmployee.CreatedUser

感謝。

Answer 1

public class CommonFields 
{ 
    public int Status { get; set; } 
    public DateTime CreatedOn { get; set; } 
    public int? CreatedById { get; set; } 
    public virtual User CreatedBy { get; set; } 
    public DateTime ModifiedOn { get; set; } 
    public virtual User ModifiedBy { get; set; } 
    public int? ModifiedById { get; set; } 
} 

，你必須在你的DbContext定義所有派生實體關係

protected override void OnModelCreating(DbModelBuilder mb) 
{ 
    mb.Entity<User>().HasOptional(x => x.CreatedBy).WithMany().HasForeignKey(x => x.CreatedById).WillCascadeOnDelete(false); 
    mb.Entity<User>().HasOptional(x => x.ModifiedBy).WithMany().HasForeignKey(x => x.ModifiedById).WillCascadeOnDelete(false); 

    mb.Entity<Employee>().HasOptional(x => x.CreatedBy).WithMany().HasForeignKey(x => x.CreatedById).WillCascadeOnDelete(false); 
    mb.Entity<Employee>().HasOptional(x => x.ModifiedBy).WithMany().HasForeignKey(x => x.ModifiedById).WillCascadeOnDelete(false); 
} 

編輯： 或者你可以使用TPH。然後你的模型創建看起來像這樣

protected override void OnModelCreating(DbModelBuilder mb) 
{ 
    mb.Entity<CommonFields>(). 
      .Map(x => x.ToTable("Users")) 
      .Map<User>(x => x.Requires("__type").HasValue(1) 
      .Map<Employee>(x => x.Requires("__type").HasValue(2); 

    mb.Entity<CommonFields>().HasOptional(x => x.CreatedBy).WithMany().HasForeignKey(x => x.CreatedById).WillCascadeOnDelete(false); 
    mb.Entity<CommonFields>().HasOptional(x => x.ModifiedBy).WithMany().HasForeignKey(x => x.ModifiedById).WillCascadeOnDelete(false); 
}