EF Core一对零关系的一种方式 [英] EF Core one-to-zero relationship one way

问题描述

可以仅以一种方式创建一对一关系吗?

Can a relationship one-to-one be created only one way?

public class Class1
{
   [Key]
   [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
   public int Class1Id { get; set; }
   ...
}

public class Class2
{
   [Key]
   [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
   public int Class2Id { get; set; }

   public int? RelationshipId { get; set; }

   public virtual Class1 Relationship { get; set; }

   ...
}

配置看起来像这样

public void Configure(EntityTypeBuilder<Class2> builder)
{
   builder.ToTable("...");

   builder.HasOne(m => m.Relationship)
     .WithOne()
     .HasForeignKey<Class1>(a => a.Class1Id);
}

但是当我尝试检查Class2实例中的Relationship时，我得到了一些错误.RelationshipId具有一个值，而Relationship.Class1Id具有不同的值.Relationship.Class1Id与Class2Id具有相同的值.

But when I try to inspect the Relationship in an instance of Class2 I get something wrong. The RelationshipId has a value and the Relationship.Class1Id has a different value. The Relationship.Class1Id has the same value as Class2Id.

为了让EF Core正常工作，是否需要Class1也具有Class2类型的属性?

Does Class1 is required to have also a property of type Class2 in order for EF Core to work correctly?

推荐答案

为了让EF Core正常工作，是否需要Class1也具有Class2类型的属性?

Does Class1 is required to have also a property of type Class2 in order for EF Core to work correctly?

不.错误在于FK映射:

No. The mistake is in FK mapping:

.HasForeignKey<Class1>(a => a.Class1Id)

这样，您告诉EF它应同时使用 Class1 的 Class1Id 属性作为 Class2 的PK和FK Class2 的 RelationshipId 属性没有被视为FK，而是像其他任何简单属性一样.

This way you are telling EF that it should use Class1Id property of the Class1 as both PK and FK to Class2, in which case the RelationshipId property of Class2 is not treated as a FK, but like any other simple property.

相反，您应该指定关系的FK属性(1)在 Class2 上，而(2)称为 RelationshipId :

Instead, you should specify the FK property of the relationship (1) is on Class2 and (2) is called RelationshipId:

builder.HasOne(e => e.Relationship)
    .WithOne()
    .HasForeignKey<Class2>(e => e.RelationshipId);
//                   ^                 ^
//                  (1)               (2)

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