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LINQ（Language-Integrated Query）是C#語言中的一個強大的查詢技術，它提供了一種統一的查詢語法，可以用于查詢和操作各種數據源，包括集合、數據庫、XML等。下面詳細描述了LINQ的20個功能點，并提供了相應的源代碼。oNr28資訊網——每日最新資訊28at.com

1. 查詢集合中的所有元素：

int[] numbers = { 1, 2, 3, 4, 5 };var query = from num in numbers            select num;foreach (var num in query){    Console.WriteLine(num);}

2. 使用條件過濾集合中的元素：

int[] numbers = { 1, 2, 3, 4, 5 };var query = from num in numbers            where num % 2 == 0            select num;foreach (var num in query){    Console.WriteLine(num);}

3. 對集合中的元素進行排序：

int[] numbers = { 5, 3, 1, 4, 2 };var query = from num in numbers            orderby num            select num;foreach (var num in query){    Console.WriteLine(num);}

4. 對集合中的元素進行分組：

string[] names = { "Alice", "Bob", "Charlie", "David", "Eve" };var query = from name in names            group name by name[0];foreach (var group in query){    Console.WriteLine(group.Key);    foreach (var name in group)    {        Console.WriteLine(name);    }}

5. 對集合中的元素進行投影：

string[] names = { "Alice", "Bob", "Charlie", "David", "Eve" };var query = from name in names            select name.Length;foreach (var length in query){    Console.WriteLine(length);}

6. 連接兩個集合的元素：

string[] names1 = { "Alice", "Bob", "Charlie" };string[] names2 = { "David", "Eve", "Frank" };var query = from name1 in names1            join name2 in names2 on name1[0] equals name2[0]            select new { Name1 = name1, Name2 = name2 };foreach (var pair in query){    Console.WriteLine($"{pair.Name1}, {pair.Name2}");}

7. 使用LINQ查詢數據庫：

using (var dbContext = new MyDbContext()){    var query = from user in dbContext.Users                where user.Age > 18                select user;    foreach (var user in query)    {        Console.WriteLine(user.Name);    }}

8. 使用LINQ查詢XML文檔：

XDocument doc = XDocument.Load("data.xml");var query = from element in doc.Descendants("book")            where (int)element.Element("price") > 10            select element.Element("title").Value;foreach (var title in query){    Console.WriteLine(title);}

9. 使用LINQ查詢JSON數據：

string json = File.ReadAllText("data.json");var data = JsonConvert.DeserializeObject<List<Person>>(json);var query = from person in data            where person.Age > 18            select person.Name;foreach (var name in query){    Console.WriteLine(name);}

10. 使用LINQ查詢并轉換結果：

int[] numbers = { 1, 2, 3, 4, 5 };var query = from num in numbers            where num % 2 == 0            select num * 2;foreach (var num in query){    Console.WriteLine(num);}

11. 使用LINQ查詢返回匿名類型：

string[] names = { "Alice", "Bob", "Charlie", "David", "Eve" };var query = from name in names            select new { Name = name, Length = name.Length };foreach (var item in query){    Console.WriteLine($"{item.Name}, {item.Length}");}

12. 使用LINQ查詢返回自定義類型：

public class Person{    public string Name { get; set; }    public int Age { get; set; }}List<Person> people = new List<Person>{    new Person { Name = "Alice", Age = 20 },    new Person { Name = "Bob", Age = 25 },    new Person { Name = "Charlie", Age = 30 }};var query = from person in people            where person.Age > 25            select person.Name;foreach (var name in query){    Console.WriteLine(name);}

13. 使用LINQ查詢返回集合：

int[] numbers = { 1, 2, 3, 4, 5 };var query = from num in numbers            where num % 2 == 0            select num * 2;List<int> result = query.ToList();foreach (var num in result){    Console.WriteLine(num);}

14. 使用LINQ進行分頁查詢：

int pageNumber = 2;int pageSize = 10;var query = from product in dbContext.Products            orderby product.Name            select product;var page = query.Skip((pageNumber - 1) * pageSize).Take(pageSize);foreach (var product in page){    Console.WriteLine(product.Name);}

15. 使用LINQ進行聚合操作：

int[] numbers = { 1, 2, 3, 4, 5 };int sum = numbers.Sum();int max = numbers.Max();int min = numbers.Min();double average = numbers.Average();Console.WriteLine($"Sum: {sum}");Console.WriteLine($"Max: {max}");Console.WriteLine($"Min: {min}");Console.WriteLine($"Average: {average}");

16. 使用LINQ進行集合的交集操作：

int[] numbers1 = { 1, 2, 3, 4, 5 };int[] numbers2 = { 4, 5, 6, 7, 8 };var query = numbers1.Intersect(numbers2);foreach (var num in query){    Console.WriteLine(num);}

17. 使用LINQ進行集合的并集操作：

int[] numbers1 = { 1, 2, 3, 4, 5 };int[] numbers2 = { 4, 5, 6, 7, 8 };var query = numbers1.Union(numbers2);foreach (var num in query){    Console.WriteLine(num);}

18. 使用LINQ進行集合的差集操作：

int[] numbers1 = { 1, 2, 3, 4, 5 };int[] numbers2 = { 4, 5, 6, 7, 8 };var query = numbers1.Except(numbers2);foreach (var num in query){    Console.WriteLine(num);}

19. 使用LINQ進行集合的連接操作：

var query = from order in dbContext.Orders            join customer in dbContext.Customers on order.CustomerId equals customer.Id            select new { OrderId = order.Id, CustomerName = customer.Name };foreach (var result in query){    Console.WriteLine($"{result.OrderId}, {result.CustomerName}");}

20. 使用LINQ進行集合的逆序操作：

int[] numbers = { 1, 2, 3, 4, 5 };var query = numbers.Reverse();foreach (var num in query){    Console.WriteLine(num);}

以上是20個常用的LINQ功能點的示例代碼，它們展示了LINQ在C#中的強大查詢能力和靈活性。通過使用LINQ，開發人員可以更加方便地進行各種數據操作和查詢，提高代碼的可讀性和開發效率。oNr28資訊網——每日最新資訊28at.com

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