为什么这个列在EF代码优先迁移中生成？ [英] Why is this column getting generated in EF Code-First migrations?

问题描述

  [必需] 
 public int MentorId {get;组; } 
 public virtual User Mentor {get;组; 
 
 [必需] 
 public int StudentId {get;组; } 
 public virtual User Student {get;组; 
  

用户模型：

  public virtual ICollection< Mentorship>导师{get;组; 
  

流利的API：

  modelBuilder.Entity< Mentorship>（）
 .HasRequired（c => c.Mentor）
 .WithMany（）
 .HasForeignKey（u => u .MentorId）; 
 
 modelBuilder.Entity< Mentorship>（）
 .HasRequired（c => c.Student）
 .WithMany（）
 .HasForeignKey（u => u.StudentId）; 
  

在我的数据库中，我看到已经正确填充的StudentId和MentorId列，但是我也看到没有被任何东西使用的User_UserId列。我做错了什么？

解决方案

你已经使用了 WithMany（）重载，将关系配置为需要：许多没有导航属性在关系的另一边 - 但你有一个导航属性在另一边的关系。

尝试这样：

  modelBuilder.Entity< Mentorship>（）
 .HasRequired（c => c .Mentor）
 .WithMany（d => d.Mentorships）
 .HasForeignKey（u => u.MentorId）; 
 
 modelBuilder.Entity< Mentorship>（）
 .HasRequired（c => c.Student）
 .WithMany（d => d.Mentorships）
 .HasForeignKey（u => u.StudentId）; // oops！只是意识到我们只是
 //指定导师正在使用MentorId 
 //作为FK 
  

参考文献：

需要与许多方法

为什么要获得额外的外键？

修改
抓住这个。只是意识到你正在尝试创建两个关系，只有一个导航属性在很多方面。您不能有2个外键的导航属性。您需要在用户侧引入继承，或从用户中删除导师属性导航属性课程或引入单独的 StudentMentorships 和 MentorMentorships 导航属性

编辑2
定义单独导航属性后查找用户

  int userId = 123; //我们要查找的
 var user = Users.Where（x => x.StudentMentorships.Any（s => s.StudentID == userId） 
 || x.MentorMentorships.Any（s => s.MentorID == userId）; 
  

I have a Mentorship entity, which has Student and Mentor as FKs:

    [Required]
    public int MentorId { get; set; }
    public virtual User Mentor { get; set; }

    [Required]
    public int StudentId { get; set; }
    public virtual User Student { get; set; }

User model:

    public virtual ICollection<Mentorship> Mentorships { get; set; }

Fluent API:

    modelBuilder.Entity<Mentorship>()
        .HasRequired(c => c.Mentor)
        .WithMany()
        .HasForeignKey(u => u.MentorId);

    modelBuilder.Entity<Mentorship>()
        .HasRequired(c => c.Student)
        .WithMany()
        .HasForeignKey(u => u.StudentId);

In my database, I see StudentId and MentorId columns which have been populated correctly, but I also see a User_UserId column that is not being used by anything. What have I done wrong?

解决方案

You have used the WithMany() overload that configures the relationship to be required:many without a navigation property on the other side of the relationship - but you do have a navigation property on the other side of the relationship.

Try this:

modelBuilder.Entity<Mentorship>()
    .HasRequired(c => c.Mentor)
    .WithMany(d => d.Mentorships)
    .HasForeignKey(u => u.MentorId);

modelBuilder.Entity<Mentorship>()
    .HasRequired(c => c.Student)
    .WithMany(d => d.Mentorships)
    .HasForeignKey(u => u.StudentId);//oops! just realised that we just 
                                     //specified that Mentorships is using MentorId 
                                     //as the FK

References:

Required WithMany Method

Why do I get an extra foreign key?

Edit Scratch that. Just realised you are trying to create two relationships with only one navigation property on the many side. You can't have a navigation property with 2 foreign keys. You need to introduce inheritance on the User side or remove the Mentorships navigation property from the User class or introduce separate StudentMentorships and MentorMentorships navigation properties

Edit 2 Finding a user once you've defined separate navigation properties

int userId = 123;//the one we want to find
var user = Users.Where(x => x.StudentMentorships.Any(s => s.StudentID == userId) 
                         || x.MentorMentorships.Any(s => s.MentorID == userId);

这篇关于为什么这个列在EF代码优先迁移中生成？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！