使用LINQ连接多个表

using System;
using System.Linq;

// 引入命名空间

namespace LinqDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            // 创建数据上下文
            var dbContext = new MyDbContext();

            // 构建LINQ查询语句
            var query = from customer in dbContext.Customers
                        join order in dbContext.Orders on customer.Id equals order.CustomerId
                        select new
                        {
                            CustomerName = customer.Name,
                            OrderId = order.Id,
                            OrderDate = order.Date
                        };

            // 执行查询
            var result = query.ToList();

            // 输出结果
            foreach (var item in result)
            {
                Console.WriteLine($"Customer: {item.CustomerName}, OrderId: {item.OrderId}, OrderDate: {item.OrderDate}");
            }
        }
    }

    // 数据上下文类
    class MyDbContext
    {
        public IQueryable<Customer> Customers { get; set; }
        public IQueryable<Order> Orders { get; set; }

        // 构造函数中初始化数据源
        public MyDbContext()
        {
            Customers = new[]
            {
                new Customer { Id = 1, Name = "Customer 1" },
                new Customer { Id = 2, Name = "Customer 2" }
            }.AsQueryable();

            Orders = new[]
            {
                new Order { Id = 1, CustomerId = 1, Date = DateTime.Now.AddDays(-1) },
                new Order { Id = 2, CustomerId = 1, Date = DateTime.Now },
                new Order { Id = 3, CustomerId = 2, Date = DateTime.Now.AddDays(-2) }
            }.AsQueryable();
        }
    }

    // 实体类
    class Customer
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

    class Order
    {
        public int Id { get; set; }
        public int CustomerId { get; set; }
        public DateTime Date { get; set; }
    }
}