对象集合查询

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

namespace UseQueryExpression
{
/// <summary>
/// 学生成绩
/// </summary>
class LessonScore
{
/// <summary>
/// 创建成绩单，传入课程名，分数
/// </summary>
public LessonScore(string les, float scr)
{
this._Lesson = les;
this._Score = scr;
}
private float _Score;
/// <summary>
/// 课程成绩
/// </summary>
public float Score
{
get
{
return this._Score;
}
}
public string _Lesson;
/// <summary>
/// 课程名称
/// </summary>
public string Lesson
{
get
{
return this._Lesson;
}
}
public override string ToString( )
{
string str;
str = string.Format("{0}---{1}分", this._Lesson, this._Score);
return str;
}
}
class Student
{

/// <summary>
/// 学生姓名
/// </summary>
private string _Name;
public string Name
{
get
{
return this._Name;
}
}

/// <summary>
/// 学生性别,男或女
/// </summary>
private string _XingBie;
public string XingBie
{
get
{
return this._XingBie;
}
}

private uint _Age;
/// <summary>
/// 学生年龄
/// </summary>
public uint Age
{
get
{
return this._Age;
}
}

private List<LessonScore> _Scores;
/// <summary>
/// 成绩单
/// </summary>
public List<LessonScore> Scores
{
get
{
return this._Scores;
}
}

/// <summary>
/// 构造函数，传入姓名，年龄，性别，成绩单。
/// </summary>
public Student(string name, string xb, uint age, List<LessonScore> scrs)
{
this._Age = age;
this._Name = name;
this._XingBie = xb;
this._Scores = scrs;
}

/// <summary>
/// 构造函数，传入姓名，年龄，性别。
/// </summary>
public Student(string name, string xb, uint age)
{
this._Age = age;
this._Name = name;
this._XingBie = xb;
this._Scores = null;
}

/// <summary>
/// 重写ToString(),获取学生的文本形式
/// </summary>
public override string ToString( )
{
string str;
str = string.Format("{0}-{1}-{2}",
this._Name, this._Age, this._XingBie);
return str;
}
}

class Program
{
static void Main(string[] args)
{
UseLeftJoin( );
}

static void UseSimpleSelect( )
{
Student[] stAry =
{
new Student("张三", "男", 20),
new Student("欧阳权宜", "男", 22),
new Student("李霞红", "女", 23),
new Student("王码码", "男", 21),
new Student("王丹", "女", 18),
};

var query1 =
from val1 in stAry
select val1;
//打印查询query1的元素
foreach (Student item in query1)
{
System.Console.WriteLine(item);
}

var query2 =
from val2 in stAry
select val2.Name;
//打印查询query2的元素
foreach (string item in query2)
{
System.Console.Write("{0},", item);
}
System.Console.WriteLine( );
var query3 =
from val3 in stAry
select val3.Name.Length;
//打印查询query3的元素
foreach (int item in query3)
{
System.Console.Write("{0},", item);
}
System.Console.WriteLine( );

var query4 =
from val4 in stAry
select new { val4.Name, val4.Age, NameLen = val4.Name.Length };
//打印查询query4的元素
foreach (var item in query4)
{
System.Console.WriteLine(item);
}
}

static void UseSimpleFrom( )
{
int[] ary = { 1, 2, 3, 5, 7 };
var query1 =
from val1 in ary
select val1;
var query2 =
from object val2 in ary
select val2;
var query3 =
from Student val3 in ary
select val3;
/*
foreach (var item in query3)
{
System.Console.WriteLine(item.ToString( ));
}
*/
}

static void UseSimpleWhere( )
{
//创建int数组ary作为数据源
int[] ary =
{ 1, 3, 9, 54, 20, 10, 23, 12, 18, 60, 37 };
//查询query1返回ary中所有大于15的元素
var query1 =
from val1 in ary
where val1 > 15
select val1;
//打印query1的数据
foreach (var item in query1)
{
System.Console.Write("{0}, ", item);
}
System.Console.WriteLine( );
//查询query2返回ary中所有大于10且小于40的元素，演示&&的使用
var query2 =
from val2 in ary
where (val2 > 10) && (val2 < 40)
select val2;
//打印查询query2的元素
foreach (var item in query2)
{
System.Console.Write("{0}, ", item);
}
System.Console.WriteLine( );
//查询query3返回ary中所有小于10或大于40的元素，演示||的使用
var query3 =
from val3 in ary
where (val3 < 10) || (val3 > 40)
select val3;
//打印查询query3的元素
foreach (var item in query3)
{
System.Console.Write("{0}, ", item);
}
System.Console.WriteLine( );
//查询query4返回ary中所有大于10且小于40的元素，演示多个where子句的使用
var query4 =
from val4 in ary
where val4 > 10
where val4 < 40
select val4;
//打印查询query4的元素
foreach (var item in query4)
{
System.Console.Write("{0}, ", item);
}
}

static void UseSimpleSort( )
{
//创建int数组ary作为数据源
int[] ary = { 9, 54, 20, 11, 3, 0, 23, 12, 18, 60, 37 };
//查询query1返回ary中所有元素，并从小到大排序
var query1 =
from val1 in ary
orderby val1
select val1;
//打印查询query1的元素
foreach (var item in query1)
{
System.Console.Write("{0}, ", item);
}
System.Console.WriteLine( );
//查询query2返回ary中所有元素，并从大到小排序
var query2 =
from val2 in ary
orderby val2 descending
select val2;
//打印查询query2的元素
foreach (var item in query2)
{
System.Console.Write("{0}, ", item);
}
}

static void UseComplexSort( )
{
//创建学生信息数组stAry作为数据源
Student[] stAry =
{
new Student("张三", "男", 20),
new Student("欧阳权宜", "男", 22),
new Student("李霞红", "女", 21),
new Student("王码码", "男", 22),
new Student("王丹", "女", 18),
};
//查询query3返回stAry中所有元素，主要按姓名字符数从小到大排序
//次要按学生姓名从大到小排序
var query3 =
from st in stAry
orderby st.Name.Length ascending, st.Age descending
select st;
//打印查询query3的元素
foreach (var item in query3)
{
System.Console.WriteLine(item);
}
}

static void UseSimpleGroupBy( )
{
//创建学生信息数组stAry作为数据源
Student[] stAry =
{
new Student("张三", "男", 20),
new Student("欧阳权宜", "男", 22),
new Student("李霞红", "女", 21),
new Student("王码码", "男", 22),
new Student("王丹", "女", 18),
};
//查询query1返回stAry中所有元素，并按照学生性别分组
var query1 =
from st in stAry
group st by st.XingBie;
//打印query1的元素
foreach (var grp in query1)
{
System.Console.WriteLine(grp.Key);
foreach (var val in grp)
{
System.Console.WriteLine("\t{0}", val);
}
}
}

static void UseComplexGroupBy( )
{
//创建学生信息数组stAry作为数据源
Student[] stAry =
{
new Student("张三", "男", 20),
new Student("欧阳权宜", "男", 22),
new Student("李霞红", "女", 20),
new Student("王码码", "男", 22),
new Student("王丹", "女", 18),
};
//查询query1返回stAry中所有元素，并按照学生年龄分组，并根据年龄从高到低排序
var query2 =
from st in stAry
group st by st.Age into stGrp
orderby stGrp.Key descending
select stGrp;
//打印query2的元素
foreach (var stGrp in query2)
{
System.Console.WriteLine("{0}岁的学生:", stGrp.Key);
foreach (var st in stGrp)
{
System.Console.WriteLine("\t{0}", st);
}
}
}

static void UseUnionFrom( )
{
//创建学生信息数组stAry作为数据源
Student[] stAry =
{
new Student("张三", "男", 20,
new List<LessonScore>{ new LessonScore("英语", 80.5f),
new LessonScore("数学", 70.0f), new LessonScore("语文", 60.5f)}),
new Student("欧阳权宜", "男", 22,
new List<LessonScore>{ new LessonScore("英语", 90.5f),
new LessonScore("数学", 80.0f), new LessonScore("语文", 50.5f)}),
new Student("李霞红", "女", 20,
new List<LessonScore>{ new LessonScore("英语", 80.5f),
new LessonScore("数学", 50.5f), new LessonScore("语文", 50.5f)}),
new Student("王码码", "男", 22,
new List<LessonScore>{ new LessonScore("英语", 50.5f),
new LessonScore("数学", 80.0f), new LessonScore("语文",40.5f)}),
new Student("王丹", "女", 18,
new List<LessonScore>{ new LessonScore("英语", 80.5f),
new LessonScore("数学", 90.0f), new LessonScore("语文", 70.5f)}),
};
//查询query1采用两个from子句实现复合查询
//第二个from子句的元素从第一个from子句的结果中再次查询
var query1 =
from st in stAry
from scr in st.Scores
where scr.Score > 80
group new { st.Name, scr } by st.Name;
//打印查询query1的元素
foreach (var grp in query1)
{
System.Console.WriteLine(grp.Key);
foreach (var item in grp)
{
System.Console.WriteLine("\t{0}", item);
}
}
}

static void UseUnionFrom2( )
{
//创建两个整数数组intAry1和intAry2作为数据源
int[] intAry1 = {5, 15, 25, 30, 33, 50};
int[] intAry2 = {10, 20, 30, 40, 50, 60, 70, 80, 90, 100};
//查询query1从两个数据源intAry1和intAry2中获取数据
var query1 =
from val1 in intAry1
from val2 in intAry2
where val2 % val1 == 0
group val2 by val1;
//打印查询query1的元素
foreach (var grp in query1)
{
System.Console.Write("{0}: ", grp.Key);
foreach (var val in grp)
{
System.Console.Write("{0} ", val);
}
System.Console.WriteLine( );
}
}

static void UseInnerJoin( )
{
//创建两个整数数组intAry1和intAry2作为数据源
int[] intAry1 = {5, 15, 25, 30, 33, 40};
int[] intAry2 = {10, 20, 30, 50, 60, 70, 80};
//查询query1使用join子句从两个数据源获取数据，演示内部联接的使用
var query1 =
from val1 in intAry1
join val2 in intAry2 on val1%5 equals val2%15
select new {VAL1=val1, VAL2=val2};
//打印查询query1的元素
foreach (var item in query1)
{
System.Console.WriteLine(item);
}
}

static void UseGroupJoin( )
{
//创建两个整数数组intAry1和intAry2作为数据源
int[] intAry1 = { 5, 15, 25, 30, 33, 40 };
int[] intAry2 = { 10, 20, 30, 50, 60, 70, 80 };
//查询query1使用join子句从两个数据源获取数据，演示分组联接的使用
var query1 =
from val1 in intAry1
join val2 in intAry2 on val1 % 5 equals val2 % 15 into val2Grp
select new { VAL1 = val1, VAL2GRP = val2Grp};
//打印查询query1的元素
foreach (var obj in query1)
{
System.Console.Write("{0}: ", obj.VAL1);
foreach (var val in obj.VAL2GRP)
{
System.Console.Write("{0} ", val);
}
System.Console.WriteLine( );
}
}

static void UseLeftJoin( )
{
//创建两个整数数组intAry1和intAry2作为数据源
int[] intAry1 = { 5, 15, 23, 30, 33, 40 };
int[] intAry2 = { 10, 20, 30, 50, 60, 70, 80 };
//查询query1使用join子句从两个数据源获取数据，演示左联接的使用
var query1 =
from val1 in intAry1
join val2 in intAry2 on val1 % 5 equals val2 % 15 into val2Grp
from grp in val2Grp.DefaultIfEmpty()
select new { VAL1 = val1, VAL2GRP = grp };
//打印查询query1的元素
foreach (var obj in query1)
{
System.Console.WriteLine("{0}", obj);
}
}
}
}