如何配置这种一对零或一对一的关系？

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我知道关于1：0..1-关系有一些已回答的问题。我看过此和此，但不要认为它们适用于我的问题

I know there are some answered questions on SO about 1:0..1-relationships. I have looked at this and this, but don't think they apply to my question.

我在CMS系统中拥有这三个（简化的）模型。

I have these three (simplified) models in a CMS-system.

public class FrontPageItem { public int Id { get; set; } public int ItemType { get; set; } // 1 = Article, 2 = WebPage, etc... public int? ArticleId { get; set; } public Article Article { get; set; } public int? WebPageId { get; set; } public WebPage WebPage { get; set; } } public class Article { public int Id { get; set; } public string Title { get; set; } public string Preamble { get; set; } public string MainText { get; set; } public int? FrontPageItemId { get; set; } public FrontPageItem FrontPageItem { get; set; } } public class WebPage { public int Id { get; set; } public string Title { get; set; } public string Content { get; set; } public int? FrontPageItemId { get; set; } public FrontPageItem FrontPageItem { get; set; } }

FrontPageItem ，每个不同的元素类型都是一对零或一个。元素可以存在而无需添加为 FrontPageItem ，这意味着 FrontPageItem 仅与一个元素相关，或者文章或网页。

The relationships between a FrontPageItem and each of the different element types are one-to-zero-or-one. An element can exist without being added as a FrontPageItem, meaning that a FrontPageItem has a relationship to just one element, either an Article or a WebPage.

为了配置关系，我添加了以下代码：

In an attempt to configure the relationships, I have added this bit of code:

protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity<Article>() .HasOne(p => p.FrontPageItem) .WithOne(i => i.Article) .HasForeignKey<FrontPageItem>(b => b.Id); modelBuilder.Entity<WebPage>() .HasOne(p => p.FrontPageItem) .WithOne(i => i.WebPage) .HasForeignKey<FrontPageItem>(b => b.Id); }

但我认为这是不正确的。我还没有为 FrontPageItem 创建CRUD视图，但是如果我尝试直接在VS的SQL Server Object Explorer中添加项目，则必须输入一个值

But I don't think it's correct. I haven't made the CRUD-views for FrontPageItem yet, but if I try to add items directly in the SQL Server Object Explorer in VS, I have to enter a value for the PK.

我在做什么错了？

推荐答案

您说：

FrontPageItem 与每种不同元素类型之间的关系一对零或一个。元素可以存在而无需添加为 FrontPageItem ，这意味着 FrontPageItem 仅与一个元素相关，或者文章或网页。

The relationships between a FrontPageItem and each of the different element types are one-to-zero-or-one. An element can exist without being added as a FrontPageItem, meaning that a FrontPageItem has a relationship to just one element, either an Article or a WebPage.

然后从 FrontPageItem 作为EF核心支持一对一或零在原则表中没有外键的关联：

Then remove ArticleId and WebPageId from FrontPageItem as EF core support one-to-one-or-zero association without foreign key in principle table:

public class FrontPageItem { public int Id { get; set; } public int ItemType { get; set; } // 1 = Article, 2 = WebPage, etc... public Article Article { get; set; } public WebPage WebPage { get; set; } }

然后为配置 Fleunt API c $ c>文章和网页如下：

Then the Fleunt API configuration for Article and WebPage as follows:

protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity<Article>() .HasOne(a => a.FrontPageItem) .WithOne(f => f.Article) .HasForeignKey<Article>(a => a.FrontPageItemId); // <-- Here it is modelBuilder.Entity<WebPage>() .HasOne(wp => wp.FrontPageItem) .WithOne(f => f.WebPage) .HasForeignKey<WebPage>(wp => wp.FrontPageItemId); // <--Here it is }