编辑“︁C Sharp LINQ 过滤”︁（章节）

== 实际应用案例 ==

=== 案例1：电子商务产品过滤 ===

假设有一个电子商务网站，需要根据用户选择的条件过滤产品：

<syntaxhighlight lang="csharp">
public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
    public string Category { get; set; }
    public int Stock { get; set; }
}

List<Product> products = new List<Product>
{
    new Product { Id = 1, Name = "Laptop", Price = 999.99m, Category = "Electronics", Stock = 10 },
    new Product { Id = 2, Name = "Smartphone", Price = 699.99m, Category = "Electronics", Stock = 15 },
    new Product { Id = 3, Name = "Desk Chair", Price = 199.99m, Category = "Furniture", Stock = 5 },
    new Product { Id = 4, Name = "Coffee Mug", Price = 9.99m, Category = "Kitchen", Stock = 20 }
};

// 用户过滤条件
decimal maxPrice = 500.00m;
string desiredCategory = "Electronics";
int minStock = 5;

var filteredProducts = products.Where(p => 
    p.Price <= maxPrice && 
    p.Category == desiredCategory && 
    p.Stock >= minStock);

Console.WriteLine("符合条件的商品:");
foreach (var product in filteredProducts)
{
    Console.WriteLine($"{product.Name} - ${product.Price}");
}
</syntaxhighlight>

'''输出:'''
<pre>
符合条件的商品:
Smartphone - $699.99
</pre>

=== 案例2：日志文件分析 ===

从日志条目中筛选出特定级别的错误：

<syntaxhighlight lang="csharp">
public class LogEntry
{
    public DateTime Timestamp { get; set; }
    public string Level { get; set; }
    public string Message { get; set; }
}

List<LogEntry> logs = new List<LogEntry>
{
    new LogEntry { Timestamp = DateTime.Now.AddHours(-1), Level = "INFO", Message = "System started" },
    new LogEntry { Timestamp = DateTime.Now.AddMinutes(-30), Level = "WARNING", Message = "Disk space low" },
    new LogEntry { Timestamp = DateTime.Now.AddMinutes(-5), Level = "ERROR", Message = "Database connection failed" }
};

// 只显示ERROR级别的日志
var errorLogs = logs.Where(log => log.Level == "ERROR");

foreach (var log in errorLogs)
{
    Console.WriteLine($"[{log.Level}] {log.Timestamp}: {log.Message}");
}
</syntaxhighlight>

'''输出:'''
<pre>
[ERROR] 5/15/2023 2:55:00 PM: Database connection failed
</pre>