实体框架中的条件包含（） [英] Conditional Include() in Entity Framework

问题描述

我已经看到了类似问题的几个答案，但是我似乎无法解决如何应用我的问题的答案。

I have seen a few answers to similar questions, however I cannot seem to work out how to apply the answer to my issue.

var allposts = _context.Posts
            .Include(p => p.Comments)
            .Include(aa => aa.Attachments)
            .Include(a => a.PostAuthor)
            .Where(t => t.PostAuthor.Id == postAuthorId).ToList();

附件可以由作者（类型作者）或贡献者（类型贡献者）上传。我想做的只是获得附件所有者的作者类型的附件。

Attachments can be uploaded by the Author (type Author) or Contributor (type Contributor). What I want to do, is only get the Attachments where the owner of the attachment is of type Author.

我知道这不起作用，并给出错误： / p>

I know this doesn't work and gives an error:

.Include(s=>aa.Attachments.Where(o=>o.Owner is Author))

我已经在这里阅读过滤投影了

I've read about Filtered Projection here

编辑 - 链接到文章：
： http://blogs.msdn.com/b/alexj/archive/2009/10/13/tip-37-how-to-do-a-conditional-include.aspx ，

EDIT - link to article: : http://blogs.msdn.com/b/alexj/archive/2009/10/13/tip-37-how-to-do-a-conditional-include.aspx,

但我只是不能让我的头脑。

but I just can't get my head around it.

我想要把最后的where子句中包含过滤器，因为我想要所有的帖子，但我只想检索属于作者的那些帖子的附件。

I don't want to include the filter in the final where clause as I want ALL posts, but I only want to retrieve the attachments for those posts that belong to the Author.

编辑2： - 发布架构请求

EDIT 2: - Post schema requested

public abstract class Post : IPostable
{

    [Key]
    public int Id { get; set; }

    [Required]
    public DateTime PublishDate { get; set; }

    [Required]
    public String Title { get; set; }

    [Required]
    public String Description { get; set; }

    public Person PostAuthor { get; set; }
    public virtual ICollection<Attachment> Attachments { get; set; }
    public List<Comment> Comments { get; set; }
}

推荐答案

从您发布的链接我可以确认诀窍是有效的，但只能用于一个（或多个）关系。在这种情况下，您的 Post-Attachment 应该是一个很多的关系，所以完全适用。这是你应该有的查询：

From the link you posted I can confirm that trick works but for one-many (or many-one) relationship only. In this case your Post-Attachment should be one-many relationship, so it's totally applicable. Here is the query you should have:

//this should be disabled temporarily
_context.Configuration.LazyLoadingEnabled = false;
var allposts = _context.Posts.Where(t => t.PostAuthor.Id == postAuthorId)
                       .Select(e => new {
                           e,//for later projection
                           e.Comments,//cache Comments
                           //cache filtered Attachments
                           Attachments = e.Attachments.Where(a => a.Owner is Author),
                           e.PostAuthor//cache PostAuthor
                        })
                       .AsEnumerable()
                       .Select(e => e.e).ToList();

这篇关于实体框架中的条件包含（）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！