EF 核心并创建多对多表。创建额外的字段。为什么？答案

【问题标题】：EF core and creating a many to many table. Creates extra field. Why ?EF 核心并创建多对多表。创建额外的字段。为什么？
【发布时间】：2018-05-18 18:41:12
【问题描述】：

为什么会有 UserProgramRefProgramCharacteristics.RefProgramCharacteristicsId 字段？？？应该只有 2 个字段而不是 3 个。对吗？下面是创建多对多表所需的 3 个类和 OnModelCreating

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

    public string ProgramCharacteristic { get; set; }

     public List<UserProgramRefProgramCharacteristic> UserProgramRefProgramCharacteristics { get; set; }

    // public ICollection<UserProgram> userPrograms { get; } = new List<UserProgram>();

   // public virtual ICollection<UserProgram> UserPrograms { get; set; }
}


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

    //UserProgramSaved
    public bool MyList { get; set; }
    public float MyPriorityRating { get; set; }
    public int Similarity { get; set; }
    public bool Compare { get; set; }

    //UserProgramSimilarity
    public int OverallSimilarityScore { get; set; }
    public int DeltaProfileElement1_WorkExp { get; set; }
    public int DeltaProfileElement2_VolExp { get; set; }
    public int DeltaProfileElement3_ResExp { get; set; }
    public int DeltaProfileElement4_Pubs { get; set; }
    public int DeltaProfileElement5_Step1 { get; set; }
    public int DeltaProfileElement6_Step2ck { get; set; }
    public int DeltaProfileElement7_Aoa { get; set; }
    public int DeltaProfileElement8_Nspecialties { get; set; }
    public int DeltaProfileElement9_PercentApps { get; set; }

    //UserComparisonSaved
    //  public RefProgramCharacteristic RefProgramCharacteristic { get; set; }
    public string RefProgramCharacteristicList { get; set; }


    public string ApplicationUserId { get; set; }
    public ApplicationUser ApplicationUser { get; set; }


    public int MedicalProgramId { get; set; }
    public RefProgramDetailData MedicalProgram { get; set; }


     public List<UserProgramRefProgramCharacteristic> UserProgramRefProgramCharacteristics { get; set; }

   // public ICollection<RefProgramCharacteristic> RefProgramCharacteristics { get; } = new List<RefProgramCharacteristic>();

   // public virtual ICollection<RefProgramCharacteristic> RefProgramCharacteristics { get; set; }


}


   public class UserProgramRefProgramCharacteristic
{
  //  public int Id { get; set; }

    public int UserProgramId { get; set; }
    public UserProgram UserProgram { get; set; }


    public int RefProgramCharacteristicsId { get; set; }
    public RefProgramCharacteristic RefProgramCharacteristic { get; set; }
}


  protected override void OnModelCreating(ModelBuilder builder)
    {
        builder.Entity<UserProgramRefProgramCharacteristic>()
            .HasKey(t => new { t.UserProgramId, t.RefProgramCharacteristicsId });

        base.OnModelCreating(builder);
    }

【问题讨论】：

标签： ef-code-first many-to-many ef-core-2.0

【解决方案1】：

为什么会有 UserProgramRefProgramCharacteristics.RefProgramCharacteristicsId 字段？

因为您告诉 EF Core 在此处创建此类字段：

public int RefProgramCharacteristicsId { get; set; }
//                                 ^

虽然导航属性被称为RefProgramCharacteristic（不是s）。还有by EF Core conventions：

如果依赖实体包含名为、或则配置为外键。

RefProgramCharacteristicsId 不匹配任何这些规则，因此 EF Core 创建一个默认名称为 RefProgramCharacteristicId 的影子 FK 属性。

要么将属性重命名为 RefProgramCharacteristicId（最佳），要么使用 ForeignKey 数据注释显式映射它：

[ForeignKey(nameof(RefProgramCharacteristicsId))]
public RefProgramCharacteristic RefProgramCharacteristic { get; set; }

或

[ForeignKey(nameof(RefProgramCharacteristic))]
public int RefProgramCharacteristicsId { get; set; }

或使用HasForeignKey fluent API：

builder.Entity<UserProgramRefProgramCharacteristic>()
    .HasOne(e => e.RefProgramCharacteristic)
    .WithMany(e => e.UserProgramRefProgramCharacteristics)
    .HasForeignKey(e => e.RefProgramCharacteristicsId);

【讨论】：