Question

我正在使用EF6，我是动态代理的忠实粉丝，可以实现延迟加载和更改跟踪。无论如何，当我首先调用枚举器或count属性时，一旦访问属性而不是加载数据，就会触发延迟加载。因此，我试图使代理变得可行，并用自定义代理替换它们。使用自定义对象上下文并重载CreateObject方法是一件容易的事情。遗憾的是，ObjectMaterialized事件无法替换实体，我无法从查询中替换实体。对象的创建深入于框架的内部类。

有人知道如何使用自定义代理吗？或者我如何能够替换对象查询中实现的实体？

Answer 1

您应该.Include要获取的属性，以避免N+1 query problem。

public class User
{
    public int Id { get; set; }
    public string Name { get; set ;}

    public virtual ICollection<Post> Posts { get; set; }
    public virtual ICollection<Comment> Comments { get; set; }
}

public class Post
{
    public int Id { get; set; }
    public string Title { get; set ; }

    public int AuthorId { get; set; }
    public virtual User Author { get; set; }

    public virtual ICollection<Comment> Comments { get; set; }
}

public class Comment
{
    public int Id { get; set; }
    public string Note { get; set ;}

    public int PostId { get; set; }
    public virtual Post Post { get; set; }

    public int AuthorId { get; set; }
    public virtual User Author { get; set; }
}

public class BlogContext : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Post> Posts { get; set; }
    public DbSet<Comment> Comments { get; set; }
}

然后这是 BAD ，因为它会进行大量查询：

using (var db = new BlogContext())
{
    var user = db.Users.Single(u => u.Id=5));  // +1 query
    foreach (var post in user.Posts) // N queries
    {
       var message = String.Format("{0} wrote {1}", user.Name, post.Title);
       Console.WriteLine(message);

       foreach (var comment in post.Comments) // N * M queries!
       {
           // and that .Author make N * M MORE!
           var message = String.Format("\t{0} commented {1}", comment.Author.Name, comment.Note);
           Console.WriteLine(message);
       }
    }
}

这是 GOOD ，因为它会一个查询：

using (var db = new BlogContext())
{
    var user = db.Users
                 .Single(u => u.Id=5))
                 .Include(u => u.Posts) // eliminates the N post queries
                 .Include(u => u.Posts.Comments) // eliminates the M comment queries
                 .Include(u => u.Posts.Comments.Author); // eliminates the M comment author queries

    foreach (var post in user.Posts) // N queries
    {
       var message = String.Format("{0} wrote {1}", user.Name, post.Title);
       Console.WriteLine(message);

       foreach (var comment in post.Comments) // N * M queries!
       {
           // and that .Author make N * M MORE!
           var message = String.Format("\t{0} commented {1}", comment.Author.Name, comment.Note);
           Console.WriteLine(message);
       }
    }
}

实体框架：POCO的自定义代理

1 个答案: