entity-framework - 自引用 1 对多关系

Question

我有以下实体:

 public class TravelCoverageType
 {
     public int Code { get; set; }

     public virtual TravelCoverageType PreventedBy { get; set; }

     public ICollection<TravelCoverageType> PreventCoverages { get; set;}
     ...
 }

每个TravelCoverageType可以阻止0个或多个TravelCoverageType。

我正在使用流畅的 API，但无法弄清楚如何描述这种关系。

我试过:

public TravelCoverageTypeConfiguration()
        {
            ToTable(ConfigConstants.TypeTablePrifix + typeof(TravelCoverageType).Name + "s");
            HasKey(ct => ct.Code);

            HasMany(tc => tc.PreventCoverages)
                .WithOptional(tc=>tc.PreventedBy)
                .HasForeignKey(tc => tc.Code);
        }  

但是我得到以下错误:

System.Data.Entity.Edm.EdmAssociationType: : Multiplicity conflicts with the referential constraint in Role 'TravelCoverageType_PreventCoverages_Source' in relationship 'TravelCoverageType_PreventCoverages'. Because all of the properties in the Dependent Role are non-nullable, multiplicity of the Principal Role must be '1'.

System.Data.Entity.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'TravelCoverageType_PreventCoverages_Target' in relationship 'TravelCoverageType_PreventCoverages'. Because the Dependent Role refers to the key properties, the upper bound of the multiplicity of the Dependent Role must be '1'.

(我添加了 PreventedBy 来简化关系的定义，我真的不需要它)

这是怎么做到的？

Answer 1

是否必须使用 Fluent API 来完成？我不太了解它，但您可以改为使用数据注释执行以下操作:

public class TravelCoverageType
{
     [Key]
     public int Code { get; set; }

     [ForeignKey("PreventedBy")]
     public int? PreventedByID { get; set; }

     public virtual TravelCoverageType PreventedBy { get; set; }

     public ICollection<TravelCoverageType> PreventCoverages { get; set;}
}

编辑:仔细观察您的问题，我注意到您正在尝试将 Code 属性用作 FK:

.HasForeignKey(tc => tc.Code);

EF 根本不喜欢这样，因为您看到的异常(exception)情况(它告诉您，如果您也想将主键设为 FK，则只能按 1:1 比例执行，而不是1:很多)。尝试向该类添加一个新属性(就像我在上面的数据注释示例中所做的那样)，然后将配置更改为:

HasMany(tc => tc.PreventCoverages)
.WithOptional(tc => tc.PreventedBy)
.HasForeignKey(tc => tc.PreventedByID);