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

一对一的关系只能以一种方式建立吗?

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; }

   ...
}

配置如下

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 实例中的关系时，我得到了一些错误.RelationshipId 有一个值，而Relationship.Class1Id 有一个不同的值.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.

是否需要 Class1 还具有 Class2 类型的属性才能使 EF Core 正常工作?

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

推荐答案

是否需要 Class1 还具有 Class2 类型的属性才能使 EF Core 正常工作?

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

没有.错误在于 FK 映射:

No. The mistake is in FK mapping:

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

这样你就告诉 EF 它应该使用 Class1 的 Class1Id 属性作为 PK 和 FK 到 Class2，在这种情况下Class2 的 RelationshipId 属性不被视为 FK，而是与任何其他简单属性一样.

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，(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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