Linq 入门系列 select篇

[ccoderlh]

其实也是对网上linq--select篇的扩充
我在这里把两种语法都写,lambda,linq写法，方便大家更好的去学习，同时也增加了一些新的东西，如解释，例子的扩充。。。
今后一段时间，我会对linq一些基本写法进行例子和解释结合的方式和大家进行分享。

 class Program
    {
        private static List<Student> GetStudents()
        {
            List<Student> students = new List<Student> { 
             new Student{ Name="YOUNG", Age=25, Language="Chinese"},
             new Student{ Name="JESSIE", Age=21, Language="Scotland"},
             new Student{ Name="KELLY", Age=18, Language="English"},
             new Student{ Name="JUNE", Age=20, Language="English"},
             new Student{ Name="ADRIAN", Age=22, Language="Italy"},
             new Student{ Name="BRUCE", Age=17, Language="Scotland"},
             new Student{ Name="BRANT", Age=30, Language="Germany"},
             new Student{ Name="BEN", Age=25, Language="Chinese"}
             };
            return students;

        }

        static void Main(string[] args)
        {
            List<Student> studentList = GetStudents();

            Select(studentList);
        }

        private static void Select<T>(T studentList)
        {
            OnlySearch(studentList);
            SearchCollectChangeOtherCollect(studentList);
            BuilderAnomy();
            BuilderAnomyExter();
            SelectLambda();
            ComplexSelect();
            ComplexSelectLambda();
        }

        private static void OnlySearch<T>(T studentList)
        {
            Console.WriteLine("<hr>只查询合适对象集合的某个属性：<br>");

            //lamb的写法
            var students = RevealChangeType(studentList).Where(n=>n.Language == "Chinese").Select(n=>n.Name);

            //linq的写法
            //var students = from n in RevealChangeType(studentList)
            //               where n.Language == "Chinese"
            //               select n.Name;

            foreach (var student in students)
            {
                Console.WriteLine(string.Format("<span class='result'>{0}</span>", student));
            }
        }

        private static IEnumerable<Student> RevealChangeType<T>(T obj)
        {
            IEnumerable<Student> student = obj as IEnumerable<Student>;

            return student;
        }

        private static void SearchCollectChangeOtherCollect<T>(T obj)
        {
            Console.WriteLine("<hr>从一个集合中查询，转化到另外一个集合：<br>");

            //age Array
            int[] intArray ={ 25, 1, 4, 3 };

            //lamb的写法
            var students = intArray.SelectMany(n=>RevealChangeType(obj).Where(s=>s.Age == n));

            //linq的写法
            //var students = from s in RevealChangeType(obj)
            //               from n in intArray
            //               where s.Age == n
            //               select s;

            foreach (var student in students)
            {
                Console.WriteLine(string.Format("<span class='result'>{0}</span>", student.Name));
            }
        }

        private static void BuilderAnomy()
        {
            Console.WriteLine("<hr>构建匿名类型：<br>");

            List<Student> studentList = GetStudents();
            int[] intArray = { 3, 1, 6, 4 };

            //lamb的写法
            var stu = intArray.Select(n=>new { Id = n, Name = (studentList as List<Student>)[n].Name });

            //linq的写法
            //var stu = from n in intArray
            //          select  new{Id = n,Name=(studentList as List<Student>)[n].Name};

            foreach (var s in stu)
            {
                Console.WriteLine(string.Format("<div class='result'>id:{0};name:{1}</div>", s.Id, s.Name));
            }
        }

        private static void BuilderAnomyExter()
        {
            Console.WriteLine("<hr>构建匿名类型2——扩展已有类：<br>");

            List<Student> studentList = GetStudents();
            int[] intArray = { 3, 1, 6, 4 };

            //lamb的写法
            var students = intArray.Select(n=>new { Id = n, studentList[n].Name, studentList[n].Age });

            //linq的写法
            //var students = from n in intArray
            //               select new {Id = n, studentList[n].Name, studentList[n].Age};

            foreach (var student in students)
            {
                Console.WriteLine(string.Format("<div class='result'>id:{0}; name:{1}; age:{2}</div>", student.Id, student.Name, student.Age));
            }
        }

        private static void SelectLambda()
        {
            Console.WriteLine("<hr>select的Lambda表达式：<br>");

            List<Student> studentList = GetStudents();
            int[] intArray = { 3, 1, 6, 4 };

            //lamb的写法
            var stu = intArray.Select(i=>new { Id = i, studentList[i].Name });

            //linq的写法
            //var stu = from i in intArray
            //          select new {Id = i, studentList[i].Name};

            foreach (var student in stu)
            {
                Console.WriteLine(string.Format("<div class='result'>id:{0}; name:{1}</div>", student.Id, student.Name));
            }
        }

        private static void ComplexSelect()
        {
            Console.WriteLine("<hr>复合选择：<br>");

            List<Student> studentList = GetStudents();
            string[] stringArray = { "Ajax", "Csharp", "Javascript", "Css Desige", "Asp.net", "Gis" };

            //lamb的写法
            //var stu = stringArray.Where(s=>s.Length > 8).SelectMany(s=>studentList.Where(str1=>str1.Age > 23).Select(str=>new { book = s, name = str.Name }));
            var stu = studentList.Where(sl=>sl.Age > 23).SelectMany(sl=>stringArray.Where(s=>s.Length > 8).Select(s=>new { name = sl.Name, book = s }));

            //linq的写法
            //var stu = from sl in studentList 
            //           where sl.Age > 23
            //           from s in stringArray 
            //           where s.Length > 8
            //           select new {name = sl.Name, book = s};

            foreach (var student in stu)
            {
                Console.WriteLine(string.Format("<div class='result'>{0} is studying {1}</div>", student.name, student.book));
            }
        }

        private static void ComplexSelectLambda()
        {
            Console.WriteLine("<hr>多重选择的Lambda表达式：<br>");

            List<Student> studentList = GetStudents();
            string[] stringArray = { "Ajax", "Csharp", "Javascript", "Css Desige", "Asp.net", "Gis" };

            //lamb的写法
            //var stu = studentList.SelectMany(s=>stringArray.Select(str => s.Name + "has a book names " + str));

            //linq的写法
            var stu = from sl in studentList                     
                      from s in stringArray                      
                      select new {name=sl.Name,language=s};

            foreach (var s in stu)
            {
                Console.WriteLine(string.Format("<div class='result'>{0}</div>", s));
            }
        }
    }

    sealed class Student
    {
        public int age;
        public int Age
        {
            get { return age; }
            set { age = value; }
        }

        private string name;
        public string Name
        {
            get { return name; }
            set { name = value; }
        }

        private string language;
        public string Language
        {
            get { return language; }
            set { language = value; }
        }
    }

[wangdetian168]

收藏看看

[priwilliam]

德国马克

[rbwang]

学习学习。。。

[jimodushi]

学习！

[yuanmanguo]

up up

[wwch369]

两种很详细,lambda语法比linq写法更简单,学习!!

[g012345678]

现在在网站在建设过程中用Linq来操作数据库的了？

[凤影]

支持。

[BernardSun]

学习

[meiZiNick]

这个简单啊,网上搜一下就得到答案了.

[UltraBejing]

有问题请先GOOGLE,BAIDU

[y51704545]

收藏

[汉升软件]

LINQ是什么東東?

[yanhuanghero]

jf

[chen_ya_ping]

楼主幸苦，学习一下。谢谢楼主分享

[雪狼孤竹]

LINQ确实是好东西，学习了！

[tianxueshan2010]

学习LINQ

[q107770540]

[Quote=引用 23 楼 blpig 的回复:]
类似于下面的查询语句用LINQ怎样写？
select * from FTable Where id in (@id)
[/Quote]
http://blog.csdn.net/q107770540/article/details/5387946

[crb0820101]

mark

[crb0820101]

mark