使用LINQ查询多个表，将结果抓取到字典中

using System;
using System.Collections.Generic;
using System.Linq;

// 定义一个学生类
class Student
{
    public int Id { get; set; }
    public string Name { get; set; }
}

// 定义一个课程类
class Course
{
    public int Id { get; set; }
    public string Name { get; set; }
}

// 定义一个成绩类
class Score
{
    public int StudentId { get; set; }
    public int CourseId { get; set; }
    public int Grade { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        // 创建学生列表
        List<Student> students = new List<Student>
        {
            new Student { Id = 1, Name = "张三" },
            new Student { Id = 2, Name = "李四" },
            new Student { Id = 3, Name = "王五" }
        };

        // 创建课程列表
        List<Course> courses = new List<Course>
        {
            new Course { Id = 1, Name = "数学" },
            new Course { Id = 2, Name = "英语" },
            new Course { Id = 3, Name = "物理" }
        };

        // 创建成绩列表
        List<Score> scores = new List<Score>
        {
            new Score { StudentId = 1, CourseId = 1, Grade = 90 },
            new Score { StudentId = 1, CourseId = 2, Grade = 85 },
            new Score { StudentId = 2, CourseId = 1, Grade = 95 },
            new Score { StudentId = 2, CourseId = 3, Grade = 80 },
            new Score { StudentId = 3, CourseId = 2, Grade = 75 },
            new Score { StudentId = 3, CourseId = 3, Grade = 88 }
        };

        // 使用LINQ查询多个表并将结果抓取到字典中
        var result = (from score in scores
                      join student in students on score.StudentId equals student.Id
                      join course in courses on score.CourseId equals course.Id
                      select new { student.Name, course.Name, score.Grade })
                     .ToDictionary(x => $"{x.Name}-{x.Course}", x => x.Grade);

        // 输出结果
        foreach (var item in result)
        {
            Console.WriteLine($"{item.Key}: {item.Value}");
        }
    }
}