Lambda表达式与标准运算符查询

class Program

{

    static void Main(string[] args)

    {

        //Lambda表达式输出List集合每一项

        List<string> list = new List<string>() { "aaa", "bbb", "ccc", "ddd", "eee" };

        list.ForEach(d => Console.WriteLine(d));

        //Lambda表达式查找匹配元素

        List<A1> a1 = new List<A1>();

        a1.Add(new A1 { Id = , Name = "aaa" });

        a1.Add(new A1 { Id = , Name = "bbb" });

        a1.Add(new A1 { Id = , Name = "ccc" });

        a1.Add(new A1 { Id = , Name = "ddd" });

        List<A1> list1 = a1.FindAll(d => d.Id > );

        //Lambda排序

        a1.Sort((x, y) => y.Id - x.Id);

        //Lambda匹配指定元素到新集合

        var s1 = a1.Select(d => new A2() { Name = d.Name });

        foreach (var item in s1)

        {

            Console.WriteLine(item.Name);

        }

        //Lambda演变过程

        var gg = new Func<string, int>(delegate(string str) { return str.Length; });

        int s = gg("abcde");

        var ss = delegate(string str) { return str.Length; };

        var qq = (string str) => { return str.Length; };

        var ww = (string str) => str.Length;

        var ee = str => str.Length;

        var bb = new Func<int, int, int>(delegate(int x, int y) { return x + y; });

        int cc = bb(,);

        Console.ReadKey();

    }

}

public class A1

{

    public int Id { get; set; }

    public string Name { get; set; }

}

public class A2

{

    public string Name { get; set; }

}

标准查询运算符-Where-Select-Order-Join

List<A1> a1 = new List<A1>();

a1.Add(new A1 { Id = , Name = "aaa", Age = , Gender = true });

a1.Add(new A1 { Id = , Name = "bbb", Age = , Gender = true });

a1.Add(new A1 { Id = , Name = "ccc", Age = , Gender = false });

a1.Add(new A1 { Id = , Name = "ddd", Age = , Gender = true });

List<DogToy> a2 = new List<DogToy>();

a2.Add(new DogToy { DogId = , DogName = "小白" });

a2.Add(new DogToy { DogId = , DogName = "小欢" });

a2.Add(new DogToy { DogId = , DogName = "小美" });

a2.Add(new DogToy { DogId = , DogName = "小王" });

//Join 连接集合

//返回的结果是一个匿名类集合，程序员可以手动的控制返回集合里使用联合查询

//两个集合里的的哪些属性

var listJoined = a1.Join(a2, d => d.Id, t => t.DogId,

    (d, t) => new { DogId = d.Id, DogName = d.Name, ToyName = t.DogName }).ToList();

listJoined.ForEach(d=>Console.WriteLine(d.ToString()));

//a1.ForEach(d => { Console.WriteLine(d.ToString()); });

//Where查询

//var aa = a1.Where(d => d.Gender == false);

//链式编程

//var aa = a1.Where(d => d.Gender == false).Select(d => new A2() { Name = d.Name });

//升序排序

//var aa = a1.OrderBy(d => d.Age).ToList();

//升序后再按指定列排序

var aa = a1.OrderBy(d => d.Age).ThenBy(d => d.Id).ToList();

//降序排序

//var aa = a1.OrderByDescending(d => d.Age).ToList();

//aa.ForEach(d => Console.WriteLine(d.ToString()));

标准查询运算符-GroupBy分组

List<A1> a1 = new List<A1>();

a1.Add(new A1 { Id = , Name = "aaa", Age = , Gender = true });

a1.Add(new A1 { Id = , Name = "bbb", Age = , Gender = true });

a1.Add(new A1 { Id = , Name = "ccc", Age = , Gender = false });

a1.Add(new A1 { Id = , Name = "ddd", Age = , Gender = false });

List<DogToy> a2 = new List<DogToy>();

a2.Add(new DogToy { DogId = , DogName = "小白" });

a2.Add(new DogToy { DogId = , DogName = "小欢" });

a2.Add(new DogToy { DogId = , DogName = "小美" });

a2.Add(new DogToy { DogId = , DogName = "小王" });

//Join 连接集合

//返回的结果是一个匿名类集合，程序员可以手动的控制返回集合里使用联合查询

//两个集合里的的哪些属性

var listJoined = a1.Join(a2, d => d.Id, t => t.DogId,

    (d, t) => new { DogId = d.Id, DogName = d.Name, ToyName = t.DogName }).ToList();

//遍历输出

listJoined.ForEach(d=>Console.WriteLine(d.ToString()));

//GroupBy分组,将姓别分组

var listGroup = a1.GroupBy(d => d.Gender);

foreach (var group in listGroup)

{

    //输出小组的分组条件

    Console.WriteLine("小组:" + group.Key);

    //遍历小组里所有的元素

    foreach (var item in group)

    {

        Console.WriteLine(item.ToString());

    }

}

//a1.ForEach(d => { Console.WriteLine(d.ToString()); });

//Where查询

var aa = a1.Where(d => d.Gender == false);

//链式编程

var aa = a1.Where(d => d.Gender == false).Select(d => new A2() { Name = d.Name });

//升序排序

var aa = a1.OrderBy(d => d.Age).ToList();

//升序后再按指定列排序

var aa = a1.OrderBy(d => d.Age).ThenBy(d => d.Id).ToList();

//降序排序

var aa = a1.OrderByDescending(d => d.Age).ToList();

aa.ForEach(d => Console.WriteLine(d.ToString()));

//分页

List<A1> a1 = new List<A1>();

a1.Add(new A1 { Id = , Name = "aaa", Age = , Gender = true });

a1.Add(new A1 { Id = , Name = "bbb", Age = , Gender = true });

a1.Add(new A1 { Id = , Name = "ccc", Age = , Gender = false });

a1.Add(new A1 { Id = , Name = "ddd", Age = , Gender = false });

var list = a1.OrderBy(d => d.Id).ToList();

//分页,Skip(0)跳过0行,Take(2)分两行

//var pageOne = list.Skip(0).Take(2);

var pageOne = list.Skip().Take().ToList();

Console.WriteLine("第一页");

pageOne.ForEach(i => Console.WriteLine(i.ToString()));

var pageTwo = list.Skip().Take().ToList();

Console.WriteLine("第二页");

pageTwo.ForEach(i => Console.WriteLine(i.ToString()));

var pageOne1 = GetPagedListByIndex(a1, );

Console.WriteLine("第一页");

pageOne1.ForEach(i => Console.WriteLine(i.ToString()));

var pageTwo2 = GetPagedListByIndex(a1, );

Console.WriteLine("第二页");

pageTwo2.ForEach(i => Console.WriteLine(i.ToString()));

Console.ReadKey();

}

//分页方法

static List<A1> GetPagedListByIndex(List<A1> groupList, int pageIndex)

{

　　int pageSize = ;

　　return groupList.Skip((pageIndex - ) * pageSize).Take(pageSize).ToList();

}

Lambda表达式与标准运算符查询的相关教程结束。