[C#] Linq 사용법

기본적으로 SQL 이랑 비슷한것같다. 예제만 늘어둘테니 알아서 익히도록

1. 3글자인 문자열 출력

using System;
using System.Linq;
namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            String[] names = new String[]{ "qq", "www","ee", "rr", "aaa"};
            var nameQuery = from name in names
                                  where name.Length == 3
                                   select name;
            foreach(string name in nameQuery) // 결과 출력
                Console.WriteLine(name);
        }
    }
}

결과는 aaa,www

2. 학생 조회

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

 

namespace test

{

    class Program

    {

        static void Main(string[] args)

        {

            //Student 객체 선언

            Student student1 = new Student();

            Student student2 = new Student();

            Student student3 = new Student();

 

            //Student형의 List 변수 student_List선언

            List<Student> student_List = new List<Student>();

 

            student1.name = "범범조조";

            student1.age = 26;

            student1.grade = 4;

 

            student2.name = "홍길동";

            student2.age = 24;

            student2.grade = 3;

 

            student3.name = "장영실";

            student3.age = 39;

            student3.grade = 2;

 

            student_List.Add(student1);

            student_List.Add(student2);

            student_List.Add(student3);

 

            //20대 학생들을 조회하는 LINQ 구문

            var Twenty_Student = from _student in student_List

                                 where _student.age >= 20 && _student.age < 30

                                 orderby _student.age ascending

                                 select _student;

 

            //30대 학생들을 조회하는 LINQ 구문

            var Thirty_Student = from _student in student_List

                                 where _student.age > 30

                                 orderby _student.age ascending

                                 select _student;

 

            foreach(var Stu in Twenty_Student)

            {

                Console.WriteLine("나이가 20대인 학생은 = {0} 입니다.", Stu.name);

            }

3. 출력할 때 배열로 뱉기

var queryStudent = from student in listAverage
                   join hobby in listHobby on student.Name equals hobby.Name
                   select new { Name = student.Name, Average = student.Average, Hobby = hobby.Hobby };
 
foreach (var studentGroup in queryStudent)
    Console.WriteLine("이름: {0}\n\t평균: {1}점\n\t취미: {2}", studentGroup.Name, studentGroup.Average, studentGroup.Hobby);