在 LINQ 查询中连接列表

发布于 2024-11-03 01:36:53 字数 607 浏览 1 评论 0原文

我的数据结构是这样设置的

一个用户使用多个模块
一个模块包含多个课程

关系如下：在此处输入图像描述

如何获取用户参加的课程列表？

我现在的查询是：

  var courses = (from ClassEnrollment enrolment in entities.ClassEnrollment
                       where enrolment.UserID == UserID
                       join Module module in entities.Module
                         on enrolment.ModuleID equals module.ID

                         select module.Course
                     ).ToList();

但是，这不会产生课程列表，而是课程列表的列表。

如何将此查询扁平化为不同课程的列表？

原文

My data structure is set up this way

A user takes a number of modules
A module contains a number of courses

Here's how the relationship looks like:
enter image description here

How do I get a list of courses the user takes?

The query I have now is:

  var courses = (from ClassEnrollment enrolment in entities.ClassEnrollment
                       where enrolment.UserID == UserID
                       join Module module in entities.Module
                         on enrolment.ModuleID equals module.ID

                         select module.Course
                     ).ToList();

However, this doesn't result in a list of courses, but rather a list of list of courses.

How can I flatten this query to a list of distinct courses?

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酷炫老祖宗 2024-11-10 01:36:53

根据您的数据结构屏幕截图，ClassEnrollment 和 Module 之间存在一对多关系，以及名为 Module 的导航属性。 Module 和 Course 之间还存在多对多关系，但导航属性应称为 Courses。给定您的代码，您想要这样的内容：

var courses = entities.
              ClassEnrollment.
              Where(e => e.UserID == UserID).
              SelectMany(e => e.Module.Courses).
              ToList();

但是，您的问题提到了一个用户：一个用户学习了多个模块，如何获取用户学习的课程列表？< /代码>。不过，我在其他地方没有看到任何 User 实体，所以如果您能澄清一下就好了。顺便说一句，您正在使用 LINQ-to-SQL 吗？

According to your data structure screenshot, you have a one-to-many relationship between the ClassEnrollment and Module, as well as navigational property called Module. You also have a many-to-many relationship between Module and Course, but the navigational property should be called Courses. Given your code, you want something like this:

var courses = entities.
              ClassEnrollment.
              Where(e => e.UserID == UserID).
              SelectMany(e => e.Module.Courses).
              ToList();

Your question, however, mentions a user: A user takes a number of modules, How do I get a list of courses the user takes?. I don't see any User entity anywhere else, though, so it would be nice if you could clarify. Are you using LINQ-to-SQL, btw?

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ら栖息 2024-11-10 01:36:53

像这样的事情：

var courses = from ClassEnrollment enrolment in entities.ClassEnrollment
              from module in entities.Module
              where enrolment.ModuleID equals module.ID && enrolment.UserID equals UserID
              select module.Course

Something like this:

var courses = from ClassEnrollment enrolment in entities.ClassEnrollment
              from module in entities.Module
              where enrolment.ModuleID equals module.ID && enrolment.UserID equals UserID
              select module.Course

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π浅易 2024-11-10 01:36:53

使用 SelectMany。

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北凤男飞 2024-11-10 01:36:53

您可以使用

course.SelectMany(c => c);

在查询中，您不需要显式指定范围变量的类型

，或者您可以将课程加入查询

var query = from enrolment in entities.ClassEnrollment
            join module in entities.Module on enrolment.ModuleID equals module.ID
            join course in entities.Course on module.CourseID equals course.ID
            where enrolment.UserID == UserID
            select course;

var course = query.ToList();

You can use

courses.SelectMany(c => c);

In your query you don't need explicitly specify the type for the range variables

Or you can join course to the query

var query = from enrolment in entities.ClassEnrollment
            join module in entities.Module on enrolment.ModuleID equals module.ID
            join course in entities.Course on module.CourseID equals course.ID
            where enrolment.UserID == UserID
            select course;

var course = query.ToList();

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