EF7不保存对象图

debugcn 发表于 Dev

克雷格（Craig W.）

我希望当我找到答案时，我会觉得自己是个白痴，但是我无法弄清楚为什么EF7不能像我以前在EF6中使用它那样保存对象图。

我的上下文是：

public class BloggingContext : DbContext, IBloggingContext
{
    public DbSet<Blog> Blogs { get; set; }
    public DbSet<Post> Posts { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Make Blog.Url required
        modelBuilder.Entity<Blog>()
            .Property(b => b.Url)
            .Required();

        modelBuilder.Entity<Post>()
            .Reference(p => p.Blog)
            .InverseCollection(b => b.Posts)
            .ForeignKey(p => p.BlogId);
    }
}

public class Blog
{
    private ICollection<Post> _posts;

    public int BlogId { get; set; }
    public string Url { get; set; }

    public virtual ICollection<Post> Posts
    {
        get
        {
            if (_posts == null)
            { _posts = new Collection<Post>(); }
            return _posts;
        }
        protected set
        { _posts = value; }

    }
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }

    public int BlogId { get; set; }

    public Blog Blog { get; set; }
}

然后，我编写以下代码：

using (var db = new BloggingContext())
{
    var blog = new Blog() { Url = DateTime.Now.ToString() };
    blog.Posts.Add(new Post() { Title = "Foo", Content = "Foo" });
    blog.Posts.Add(new Post() { Title = "Bar", Content = "Bar" });

    db.Blogs.Add(blog);
    var count = db.SaveChanges();

    Console.WriteLine("{0} records saved to database", count);

    return blog.BlogId;
}

之后SaveChanges就是所谓的blog对象有一个BlogId，但BlogId在这两个Post对象仍然是-1，没有被添加到数据库中。