C# LINQ：简化集合查询（基础用法）

LINQ（Language Integrated Query）是集成在 C# 中的查询语言，可简洁地查询集合、数据库等数据源。
public class LinqDemo
{
public static void QueryList()
{
// 数据源：产品列表
List products = new List
{
new Product { Id = 1, Name = "C#教程", Price = 99.9m, Category = "图书" },
new Product { Id = 2, Name = "键盘", Price = 199.9m, Category = "数码" },
new Product { Id = 3, Name = "鼠标", Price = 89.9m, Category = "数码" },
new Product { Id = 4, Name = "Java教程", Price = 89.9m, Category = "图书" },
new Product { Id = 5, Name = "显示器", Price = 1299.9m, Category = "数码" }
};

    // 1. 查询所有数码类产品（Where）
    var digitalProducts = products.Where(p => p.Category == "数码");
    Console.WriteLine("=== 数码类产品 ===");
    foreach (var p in digitalProducts)
    {
        Console.WriteLine($"{p.Name} - {p.Price:C}");
    }

    // 2. 查询价格低于100元的产品，按价格升序排序（Where + OrderBy）
    var cheapProducts = products.Where(p => p.Price < 100).OrderBy(p => p.Price);
    Console.WriteLine("\n=== 价格低于100元的产品（升序） ===");
    foreach (var p in cheapProducts)
    {
        Console.WriteLine($"{p.Name} - {p.Price:C}");
    }

    // 3. 按分类分组（GroupBy）
    var groupedByCategory = products.GroupBy(p => p.Category);
    Console.WriteLine("\n=== 按分类分组 ===");
    foreach (var group in groupedByCategory)
    {
        Console.WriteLine($"分类：{group.Key}");
        foreach (var p in group)
        {
            Console.WriteLine($"  - {p.Name}");
        }
    }

    // 4. 投影（只取名称和价格，匿名类型）
    var productInfo = products.Select(p => new { p.Name, p.Price });
    Console.WriteLine("\n=== 产品名称和价格 ===");
    foreach (var info in productInfo)
    {
        Console.WriteLine($"{info.Name}：{info.Price:C}");
    }

    // 5. 统计（Count/Sum/Average）
    int totalCount = products.Count();
    decimal totalPrice = products.Sum(p => p.Price);
    decimal avgPrice = products.Average(p => p.Price);
    Console.WriteLine($"\n=== 统计信息 ===");
    Console.WriteLine($"产品总数：{totalCount}");
    Console.WriteLine($"总价：{totalPrice:C}");
    Console.WriteLine($"均价：{avgPrice:C}");
}

}

// 产品实体类
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public decimal Price { get; set; }
public string Category { get; set; }
}

// 调用示例
LinqDemo.QueryList();