集合查询和查询结果处理

一、环境准备

1、创建俩个包含集合的类MartialArtsMaster和Kongu

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace LINQ查询
{class MartialArtsMaster{public int Id { get; set; }public string Name { get; set; }public int Age { get; set; }public string Menpai { get; set; }public string Kongfu { get; set; }public int Level { get; set; }public override string ToString(){return string.Format("Id: {0}, Name: {1}, Age: {2}, Menpai: {3}, Kongfu: {4}, Level: {5}", Id, Name, Age, Menpai, Kongfu, Level);}}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace LINQ查询
{class Kongfu{public int Id { get; set; }public string Name { get; set; }public int Power { get; set; }public override string ToString(){return string.Format("Id: {0}, Name: {1}, Power: {2}", Id, Name, Power);}}
}

2、创建集合

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace LINQ查询
{class Program{static void Main(string[] args){List<MartialArtsMaster> Mam = new List<MartialArtsMaster>(){new MartialArtsMaster() {Id = 1, Name = "黄蓉", Age = 18, Menpai = "丐帮", Kongfu = "打狗棒法", Level = 9},new MartialArtsMaster() {Id = 2, Name = "洪七公", Age = 70, Menpai = "丐帮", Kongfu = "打狗棒法", Level = 10},new MartialArtsMaster() {Id = 3, Name = "郭靖", Age = 22, Menpai = "丐帮", Kongfu = "降龙十八掌", Level = 10},new MartialArtsMaster() {Id = 4, Name = "任我行", Age = 50, Menpai = "明教", Kongfu = "葵花宝典", Level = 1},new MartialArtsMaster() {Id = 5, Name = "东方不败", Age = 35, Menpai = "明教", Kongfu = "葵花宝典", Level = 10},new MartialArtsMaster() {Id = 6, Name = "林平之", Age = 23, Menpai = "华山", Kongfu = "葵花宝典", Level = 7},new MartialArtsMaster() {Id = 7, Name = "岳不群", Age = 50, Menpai = "华山", Kongfu = "葵花宝典", Level = 8},new MartialArtsMaster() {Id = 8, Name = "令狐冲", Age = 23, Menpai = "华山", Kongfu = "独孤九剑", Level = 10},new MartialArtsMaster() {Id = 9, Name = "梅超风", Age = 23, Menpai = "桃花岛", Kongfu = "九阴真经", Level = 8},new MartialArtsMaster() {Id = 10, Name = "黄药师", Age = 23, Menpai = "梅花岛", Kongfu = "弹指神通", Level = 10},new MartialArtsMaster() {Id = 11, Name = "风清扬", Age = 23, Menpai = "华山", Kongfu = "独孤九剑", Level = 10}};List<Kongfu> Kf = new List<Kongfu>() {new Kongfu() {Id = 1, Name = "打狗棒法", Power = 90},new Kongfu() {Id = 2, Name = "降龙十八掌", Power = 95},new Kongfu() {Id = 3, Name = "葵花宝典", Power = 100},new Kongfu() {Id = 4, Name = "独孤九剑", Power = 100},new Kongfu() {Id = 5, Name = "九阴真经", Power = 100},new Kongfu() {Id = 6, Name = "弹指神通", Power = 100}};

二、使用LINQ查询

1、标准写法

            var res = from m in Mamfrom k in Kfwhere m.Kongfu == k.Nameselect  m;//select new{mam = k, kf = k};

该查询从同时从Man和Kf中查询，即俩个集合互相遍历查询？where后面跟查询筛选条件，select 后面跟输出的集合。可以使用new 输出一个组合,如注释行所示。

2、单个集合查询的扩展写法

var res = Mam.Where(delegate (MartialArtsMaster m) { return m.Id > 5; });//使用匿名函数版本
var res = Mam.Where(a =>  a.Id > 5 );//使用Lambda版本

3、多个集合查询的扩展写法，看不懂不建议用！！！请用标准的多个集合查询写法！！！

     var res = Mam.SelectMany(m => Kf, (m, k) => new { master = m, kongfu = k }).Where(x => x.master.Kongfu == x.kongfu.Name);

三、LINQ查询时返回排序结果

标准写法

            var res = from m in Mam orderby m.Age, m.Level//可选单一或多个排序方式，优先级以第一个最高往后依次递减select m;

扩展写法

            var res = Mam.Where(m => m.Level > 1).OrderBy(m => m.Level).ThenBy(m=>m.Age);

四、JOIN连接查询

1、

            var res = from m in Mamjoin k in Kf on m.Kongfu equals k.Name //当m.Kongfu 中与 k.Name能匹配的m和k被保留下来//Man连接Kfwhere m.Level>8select new { mam = m, kongfu = k };

3、JOIN连接单个查询并分组

             var res = from m in Mamgroup m by m.Menpai into Gorderby G.Count()select new { cont = G.Count(), key = G.Key };

4、JOIN连接查询并分组

            var res = from k in Kfjoin m in Mam on k.Name equals m.Kongfu //k连接m 在on后面只能先写k再写minto g //将匹配结果保存到g集合完成分组操作orderby g.Count()select new { kongfu = k, conunt = g.Count() };

五、量词操作符Any 和 All

            bool i = Mam.Any(m => m.Menpai == "华山");//当集合中存在元素符合条件时返回truevar res = from m in Mamwhere m.Menpai == "华山"select m;bool n = res.All(m => m.Menpai == "华山");//当集合中所有元素符合条件时返回true

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