EF LINQ 包括多个和嵌套的实体 [英] EF LINQ include multiple and nested entities

问题描述

好的，我有具有以下层次结构的三层实体:课程 -> 模块 -> 章节

Ok, I have tri-leveled entities with the following hierarchy: Course -> Module -> Chapter

这是原始的 EF LINQ 语句:

Here was the original EF LINQ statement:

Course course = db.Courses
                .Include(i => i.Modules.Select(s => s.Chapters))
                .Single(x => x.Id == id); 

现在，我想包含另一个与课程相关的名为 Lab 的实体.

Now, I want to include another entity called Lab which is associated with a course.

如何包含实验室实体?

我尝试了以下方法，但没有奏效:

I tried the following but it didn't work:

Course course = db.Courses
                .Include(i => i.Modules.Select(s => s.Chapters) && i.Lab)
                .Single(x => x.Id == id); 

关于包含第二个实体的任何想法?

Any ideas on including the 2nd Entity?

任何建议或信息将不胜感激.谢谢！

Any piece of advise or information would be highly appreciated. Thanks!

推荐答案

您是否尝试过仅添加另一个 Include:

Have you tried just adding another Include:

Course course = db.Courses
                .Include(i => i.Modules.Select(s => s.Chapters))
                .Include(i => i.Lab)
                .Single(x => x.Id == id);

您的解决方案失败了，因为 Include 没有使用布尔运算符

Your solution fails because Include doesn't take a boolean operator

Include(i => i.Modules.Select(s => s.Chapters) &&          i.Lab)
                           ^^^                  ^             ^ 
                          list           bool operator    other list

更新要了解更多信息，请下载 LinqPad 并浏览示例.我认为这是熟悉 Linq 和 Lambda 的最快方法.

Update To learn more, download LinqPad and look through the samples. I think it is the quickest way to get familiar with Linq and Lambda.

首先 - Select 和 Include 之间的区别在于，通过 Select，您可以决定什么你想返回(又名投影).Include 是一个 Eager Loading 函数，它告诉实体框架您希望它包含来自其他表的数据.

As a start - the difference between Select and Include is that that with a Select you decide what you want to return (aka projection). The Include is a Eager Loading function, that tells Entity Framework that you want it to include data from other tables.

Include 语法也可以是字符串.像这样:

The Include syntax can also be in string. Like this:

           db.Courses
            .Include("Module.Chapter")
            .Include("Lab")
            .Single(x => x.Id == id);

但是 LinqPad 中的示例更好地解释了这一点.

But the samples in LinqPad explains this better.

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