如何在Entity Framework + SQL Server中实施一对一关系

Question

Building my own mini CMS back end in EF + SQL Server (Database First). I have a "Contents" table which all entities link too using a Foreign Key.

CREATE TABLE [dbo].[Contents](
[ContentID] [int] IDENTITY(1,1) NOT NULL,
[ContentType] [varchar](100) NOT NULL,
[DateAdded] [datetime] NOT NULL,
[DateUpdated] [datetime] NULL,
[isDeleted] [bit] NOT NULL,
[UserId] [int] NOT NULL

CREATE TABLE [dbo].[Articles](
[ArticleID] [int] IDENTITY(1,1) NOT NULL,
[ContentID] [int] NOT NULL,
[ImageID] [int] NOT NULL,
[ArticleHeadline] [varchar](250) NOT NULL,
[ArticleSummary] [nvarchar](200) NOT NULL,
[ArticleBody] [nvarchar](500) NOT NULL

ALTER TABLE [dbo].[Articles]  WITH CHECK ADD  CONSTRAINT [FK_Articles_Contents] FOREIGN KEY([ContentID])
REFERENCES [dbo].[Contents] ([ContentID])

In Entity Framework the Entity Content quite rightly thinks that this is a one to many relationship. How do I go about making this one to one? Content can only belong to one other Entity but I keep having to use First() in my code.

<h1>@Model.Content.Articles.First().ArticleHeadline</h1>
@Html.Raw(Model.Content.Articles.First().ArticleBody)

Answer 1

As for database first approach, to have 1-1 association in EF, the dependent ([dbo].[Articles]) must have a primary key that also is the foreign key to the principal([dbo].[Contents]). It will require some DB design change like this:

CREATE TABLE [dbo].[Contents](
[ContentID] [int] NOT NULL PRIMARY KEY,
[ContentType] [VARCHAR](100) NOT NULL
)

CREATE TABLE [dbo].[Articles](
[ContentID] [int] NOT NULL PRIMARY KEY, 
[ImageID] [int] NOT NULL,
CONSTRAINT [FK_Contents] FOREIGN KEY ([ContentID]) REFERENCES [dbo].[Contents] ([ContentID]) ON DELETE CASCADE
)

Answer 2

This should answer your question http://www.entityframeworktutorial.net/code-first/configure-one-to-one-relationship-in-code-first.aspx

Look at the fluent configuration

    protected override void OnModelCreating(DbModelBuilder modelBuilder) {
     // Configure StudentId as PK for StudentAddress 

modelBuilder.Entity<StudentAddress>() .HasKey(e => e.StudentId); 
    // Configure StudentId as FK for StudentAddress 

modelBuilder.Entity<StudentAddress>() .HasRequired(ad => ad.Student) .WithOptional(s => s.StudentAddress); }

Replace student address and student with article content and article

For db first mappings you will need to modify your edmx and regenerate your models.

This may help: http://www.exceptionnotfound.net/entity-framework-for-beginners-creating-a-database-first-model/