实体框架1-To-*和1-to-1

Question

(实体框架6,.NET 4,VS 2010)

我创建了一个小型的Blog项目来说明问题.这是一个博客,有很多帖子,但只有一个帖子作为主要帖子.

public class Blog
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Post> PostEntities { get; set; }

    public int? MainPostId { get; set; }

    [ForeignKey("MainPostId")]
    public virtual Post MainPostEntity { get; set; }  // Problem here
}

public class Post
{
    public int Id { get; set; }
    public int BlogId { get; set; }
    [ForeignKey("BlogId")]
    public virtual Blog BlogEntity { get; set; }
    public string Title { get; set; }
}

modelBuilder.Entity<Blog>()
    .HasOptional(b => b.MainPostEntity)
    .WithRequired(p => p.BlogEntity);

static void Main(string[] args)
{
    Database.SetInitializer<EFTestContext>(null);
    EFTestContext db = new EFTestContext();
    Post[] posts = db.Posts.ToArray(); // Error here
}

如果我删除导航属性,public virtual Post MainPostEntity一切都按预期工作.但是,当我添加它时,我得到:

base {System.SystemException} = {"The ForeignKeyAttribute on property 'MainPostEntity' on type 'EFTest.Blog' is not valid. The foreign key name 'MainPostId' was not found on the dependent type 'EFTest.Post'. The Name value should be a comma separated list of foreign key property names."}

如果我删除了流畅的API调用,我会得到 {"Invalid column name 'Blog_Id'."}

如果我将属性更改[ForeignKey("MainPostId")]为[ForeignKey("Id")]I,则会出现以下错误{"Invalid column name 'Blog_Id'."}

我究竟做错了什么？如何从Blog启用导航属性到主帖？

Answer 1

您遇到的问题是，您在相同的两个表之间创建两个关系，而 EF 无法区分导航属性BlogEntity属于哪个关系。使用 Fluent api，您可以明确地告诉它，这样就不需要数据注释了。

modelBuilder.Entity<Blog>().HasMany(b => b.PostEntities).
                            WithRequired(p => p.BlogEntity).
                            HasForeignKey(p => p.BlogId).
                            WillCascadeOnDelete(true);

modelBuilder.Entity<Blog>().HasOptional(b => b.MainPostEntity).
                            WithMany().
                            HasForeignKey(b => b.MainPostId).
                            WillCascadeOnDelete(false);