c# - 如何在实体中的两个字段（在同一个表或不同）之间设置一个方向关系

Question

我正在使用 CodeFirst 进行开发。对于我的实体中的所有模型类，我有一个名为 CommonFields 的基类

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。我有两个类

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
}

如何设置从 CreatedBy 和 ModifiedBy 到用户表的关系。我只需要一个方向映射。

写 objEmployee.CreatedUser 时需要获取用户信息

谢谢。

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; }
}

并且您必须为 DbContext 中的所有派生实体定义关系

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);
}

编辑： 或者你可以使用 TPH。然后你的模型创建看起来像这样

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);
}