EF Linq查询与条件包括 [英] EF Linq query with conditional include

问题描述

所以我有以下的Linq查询：

So I have the following Linq query:

var member = (from mem in 
              context.Members.Include(m => 
              m.MemberProjects.Select(mp => mp.Project))
              where mem.MemberId == memberId
             select mem).FirstOrDefault();

这将返回一个成员实体，一组具有Project子项的MemberProjects。我想限制MemberProjects只有那些Project项目的子项有一个属性
ProjectIdParent == null 。

This returns a Member entity, with a set of MemberProjects that have a Project child. I would like to limit the MemberProjects to only those for which the Project child has a property ProjectIdParent == null.

我的一个失败的尝试可能会使意图更清楚：

One of my failed attempts might make the intent clearer:

var member = (from mem in context.Members
             .Include(m => m.MemberProjects
                            .Where(mp => 
                                   mp.Project.ProjectIdParent == null)
             .Select(proj => proj.Project))
             where mem.MemberId == memberId
             select mem).FirstOrDefault();

这当然是因为Where子句而引起无效的包含表达式。

This of course complains of an invalid Include expression because of the Where clause.

任何关于如何做到这一点的想法将是很棒的：）

Any thoughts on how to do this would be great :)

推荐答案

免责声明：我没有测试过这个。这只是一个想法。如果你让我知道结果，我会相应地更新。 （跳到更新部分获取测试解决方案）

DISCLAIMER: I havent tested this. This is just an idea. If you let me know the results, I will update this accordingly. (Skip to the update part for the tested solutions)

var member = (from mps in context.MemberProjects
                                .Include(m => m.Members)
                                .Include(m => m.Projects)  
              where mps.Project.ProjectIdParent == null
              select mps)
              .FirstOrDefault(mprojs => mprojs.Member.MemberId == memberId);     

我还会使用类似 EFProfiler ，以确保生成的查询不会离开理智的境界。

I'd also analyze the queries using something like EFProfiler to make sure the generated queries dont leave the realm of sanity.

你可以还要看看这篇文章由Jimmy Bogard发表了许多与ORM的关系。

You can also take a look at this post by Jimmy Bogard on Many to Many relationships with ORMs.

更新

我为EF 6.1提出了多项测试解决方案0.3。我的Edmx如下所示：

I came up with multiple tested solutions for this with EF 6.1.3. My Edmx looked like below:

设置数据如下所示：

我能够运行下面的代码来正确获取MemberFive

I was able to run code below to get the MemberFive correctly

var member = context.Members.FirstOrDefault
                     (m => m.MemberId == memberId 
                         && m.Projects.Any(p => p.ProjectParentId == null));

生成的SQL如下所示：

The generated SQL looked like this:

SELECT TOP (1) [Extent1].[MemberId]   AS [MemberId],
           [Extent1].[MemberName] AS [MemberName]
FROM   [dbo].[Members] AS [Extent1]
WHERE  ([Extent1].[MemberId] = 1)
   AND (EXISTS (SELECT 1 AS [C1]
                FROM   (SELECT [MemberProjects].[MemberId]  AS [MemberId],
                               [MemberProjects].[ProjectId] AS [ProjectId]
                        FROM   [dbo].[MemberProjects] AS [MemberProjects])     
           AS [Extent2]
                       INNER JOIN [dbo].[Projects] AS [Extent3]
                         ON [Extent3].[ProjectId] = [Extent2].[ProjectId]
                WHERE  ([Extent1].[MemberId] = [Extent2].[MemberId])
                       AND ([Extent3].[ProjectParentId] IS NULL)))

如果你不喜欢生成的查询，你可以使用这个：

If you dont like the generated query you can use this:

 var memberQuery = @"Select M.* from Members M
                            inner join MemberProjects MP on M.MemberId = Mp.ProjectId
                            inner join Projects P on MP.ProjectId = P.ProjectId
                            where M.MemberId = @MemberId and P.ProjectParentId is NULL";
 var memberParams = new[]
                     {
                      new SqlParameter("@MemberId", 1)
                     };
 var member3 = context.Members.SqlQuery(memberQuery, memberParams)
               .FirstOrDefault();

后来一直在20ms内返回，另一个在60ms左右徘徊（如果对您很重要）。

The later consistently returned under 20ms vs the other one hovered around 60ms (if that matters to you).

我希望这有助于。

这篇关于EF Linq查询与条件包括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！