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所属分类：.NET技术
LINQ（Language-Integrated Query）是C#语言中的一个强大的查询技术，它提供了一种统一的查询语法，可以用于查询和操作各种数据源，包括集合、数据库、XML等。下面详细描述了LINQ的20个功能点，并提供了相应的源代码。
- 查询集合中的所有元素：
int[] numbers = { 1, 2, 3, 4, 5 }; var query = from num in numbers select num; foreach (var num in query) { Console.WriteLine(num); }- 使用条件过滤集合中的元素：
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); }- 对集合中的元素进行排序：
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); }- 对集合中的元素进行分组：
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); } }- 对集合中的元素进行投影：
string[] names = { "Alice", "Bob", "Charlie", "David", "Eve" }; var query = from name in names select name.Length; foreach (var length in query) { Console.WriteLine(length); }- 连接两个集合的元素：
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($"{pair.Name1}, {pair.Name2}"); }- 使用LINQ查询数据库：
using (var dbContext = new MyDbContext()) { var query = from user in dbContext.Users where user.Age > 18 select user; foreach (var user in query) { Console.WriteLine(user.Name); } }- 使用LINQ查询XML文档：
XDocument doc = XDocument.Load("data.xml"); var query = from element in doc.Descendants("book") where (int)element.Element("price") > 10 select element.Element("title").Value; foreach (var title in query) { Console.WriteLine(title); }- 使用LINQ查询JSON数据：
string json = File.ReadAllText("data.json"); var data = JsonConvert.DeserializeObject<List<Person>>(json); var query = from person in data where person.Age > 18 select person.Name; foreach (var name in query) { Console.WriteLine(name); }- 使用LINQ查询并转换结果：
int[] numbers = { 1, 2, 3, 4, 5 }; var query = from num in numbers where num % 2 == 0 select num * 2; foreach (var num in query) { Console.WriteLine(num); }- 使用LINQ查询返回匿名类型：
string[] names = { "Alice", "Bob", "Charlie", "David", "Eve" }; var query = from name in names select new { Name = name, Length = name.Length }; foreach (var item in query) { Console.WriteLine($"{item.Name}, {item.Length}"); }- 使用LINQ查询返回自定义类型：
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); }- 使用LINQ查询返回集合：
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); }- 使用LINQ进行分页查询：
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); }- 使用LINQ进行聚合操作：
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}");- 使用LINQ进行集合的交集操作：
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); }- 使用LINQ进行集合的并集操作：
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); }- 使用LINQ进行集合的差集操作：
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); }- 使用LINQ进行集合的连接操作：
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}"); }- 使用LINQ进行集合的逆序操作：
int[] numbers = { 1, 2, 3, 4, 5 }; var query = numbers.Reverse(); foreach (var num in query) { Console.WriteLine(num); }以上是20个常用的LINQ功能点的示例代码，它们展示了LINQ在C#中的强大查询能力和灵活性。通过使用LINQ，开发人员可以更加方便地进行各种数据操作和查询，提高代码的可读性和开发效率。
