多对多查询实体框架4 [英] Many to Many Query in Entity Framework 4

问题描述

我有一个多对多的关系在我的数据库。两个端表是博文和项目，并在中间表ItemBlogPost。我需要找回所有与特定项目相关博客文章的。在SQL中我会做这样的：

I have have a many to many relationship in my database. The two end tables are BlogPost and Item and the table in the middle is ItemBlogPost. I need to get back all of the BlogPosts related to a specific item. In SQL I would do it like this:

SELECT BlogPost.*
FROM BlogPost
    JOIN ItemBlogPost ON BlogPost.ID = ItemBlogPost.BlogPost_ID
WHERE ItemBlogPost.Item_ID = @Item_ID

在C＃中我有类似的东西：

In C# I have something similar:

IQueryable<BlogPost> itemBlogPosts = from b in connection.BlogPosts
                                     where b.Items == item.ID 
                                     orderby b.Content.CreateDate descending
                                     select b;

然而，行标b.Items不给我的项目属性的列表，并且没有b.ItemBlogPost看中间表。我也试着做 b.Items.Contains（项目）但也失败了。我怎样才能使这项工作在LINQ to EF4？

However, the line marked b.Items doesn't give me a list of the Item properties and there is no b.ItemBlogPost to look at the intermediary table. I also tried doing b.Items.Contains(item) but that also failed. How can I make this work in LINQ to EF4?

推荐答案

这个是什么：

var itemBlogPosts = from i in connection.Items
                    from b in i.BlogPosts // I suppose you have a nav. property on Item
                    where i.Id == itemId
                    select b; 

同样的查询可以通过还定义：

The same query can be also defined by:

var itemBlogPosts = connection.Items
                              .Where(i => i.Id == itemId)
                              .SelectMany(i => i.BlogPosts);

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