LINQ 操作符（二）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Lambda表达式
{
    class Program
    {
        static void Main(string[] args)
        {

        }
        static List<Person> GetPersonList()
        {
            return new List<Person>() { 
            new Person (){ Age =1,Name ="小白01",ID=1,Gender =true},
            new Person (){Age =2,Name ="小白02",ID=2,Gender =false},
            new Person (){Age =3,Name ="小白03",ID=3,Gender =true}
            };
        }

        static List<PersonToy> GetPersonToyList()
        {
            return new List<PersonToy>() { 
            new PersonToy(){ PersonToyID=1,Name="小明"},
            new PersonToy (){PersonToyID =2,Name ="小白"},
            new PersonToy (){PersonToyID =3,Name ="小红"},
            new PersonToy (){PersonToyID =4,Name ="小黑"}
            };
        }

        #region Lambda表达式
        /// <summary>
        /// Lambda表达式和Lambda语句
        /// </summary>
        static void TestLambda()
        {
            List<Person> list = GetPersonList();
            list.ForEach(d => Console.WriteLine(d.Name));
            //Lambda表达式
            list.FindAll(d => d.Age > 1);
            list.Sort((x, y) => x.Age - y.Age);
            var it = list.Select(p => new smallperson { Name = p.Name });
            //语句Lambda语句
            var it1 = list.Select(p =>
            { //如果存在多个语句就不能省略{}大括号 也不能省略return
                smallperson sp = new smallperson();
                sp.Name = p.Name;
                return sp;
            });
        }
        #endregion

        /// <summary>
        /// 标准查询方法 ----Where查询
        /// </summary>
        static void SQOWhere()
        {
            List<Person> list = GetPersonList();
            //在集合中筛选出符合条件的数据
            List<Person> list2 = list.Where(p => p.Gender == false && p.Age > 1 && p.Age < 3).ToList();
            list.ForEach(p => Console.WriteLine(p.Name));
        }

        /// <summary>
        /// 标准查询运算符 select 投射方法（返回一个新的集合）
        /// </summary>
        static void SQOSelect()
        {
            List<Person> list = GetPersonList();
            List<smallperson> list2 = list.Where(p => p.Gender == false).Select(p => new smallperson() { Name = p.Name }).ToList();
        }

        /// <summary>
        /// 标准查询运算符 Order 排序方法 返回一个新的集合
        /// </summary>
        static void SQOOrder()
        {
            List<Person> list = GetPersonList();
            List<Person> listSorted = list.OrderBy(p => p.Age).ThenByDescending(p => p.ID).ToList();//按照年龄进行排序（升序）
            // list .OrderByDescending 倒序

            list.ForEach(p => Console.WriteLine(p.Age.ToString()));
        }

        /// <summary>
        /// 标准运算符--连接集合
        /// </summary>
        static void TestJoin()
        {
            List<Person> listperson = GetPersonList();
            List<PersonToy> listPersontToy = GetPersonToyList();
            var listJoin = listperson.Join(listPersontToy, d => d.ID, t => t.PersonToyID, (d, t) => new { ID = d.ID, ToyName = t.Name, Name = d.Name }).ToList();

            listJoin.ForEach(a => Console.WriteLine(a.ID.ToString() + "," + a.ToyName));
        }

        /// <summary>
        /// 标准查询运算符 GroupBy为集合分组
        /// 
        /// </summary>
        static void SQOGroupBy()
        {
            List<Person> list = GetPersonList();
            //按照性别进行分组
            IEnumerable<IGrouping<bool, Person>> it = list.GroupBy(p => p.Gender);

            //根据姓名进行分组
            IEnumerable<IGrouping<string, Person>> it2 = list.GroupBy(p => p.Name);
            // var it2= list.GroupBy(p=>p.Name );

            IList<IGrouping<bool, Person>> listGroup = it.ToList();
            foreach (var group in listGroup)
            {
                Console.WriteLine(group.Key.ToString());
                foreach (var item in group)
                {
                    Console.WriteLine(item.Name + "," + item.Age);
                }
                Console.WriteLine("------------------------------------");
            }
        }

        /// <summary>
        /// 标准运算符=Skip -Take分页数据
        /// </summary>
        static void SQOPagedList()
        {
            List<Person> list = GetPersonList();
        }

        /// <summary>
        ///Linq语句 ，编译后会生成对应的标准查询 运算符 linq是一种类似sql的一种更加友好的语法糖 语法而已
        /// </summary>
        static void TestLinq()
        {
            List<Person> list = GetPersonList();
            List<PersonToy> listtoy = GetPersonToyList();
            var query = from li in list select li;//从老集合中每一个元素 存入一个新的集合
            //where
            var query1 = from li in list where li.Gender == true select li;
            //order descending倒序 aescending正序
            var query2 = from li in list orderby li.Gender orderby li.Age descending select li;
            //join链接查询
            var query3 = from li in list join t in listtoy on li.ID equals t.PersonToyID select new { Name = li.Name };
            //分组查询
            var query4 = from li in list group li by li.Gender;

        }

    }
    public class smallperson
    {
        public string Name { get; set; }
    }
}