LINQ查询表达式---------select子句
1.1常见的select子句查询
class Program
{
public class PerInfo
{
public int Id
{
get;
set;
}
public string Name
{
get;
set;
}
public int Age
{
get;
set;
}
public List<int> Scores
{
get;
set;
}
}
List<PerInfo> PerInfos = new List<PerInfo>()
{
new PerInfo
{
Id = 1, Name = "小白", Age = 15, Scores = new List<int>()
{
78, 88, 95, 60
}
},
new PerInfo
{
Id = 2, Name = "小日", Age = 18, Scores = new List<int>()
{
98, 86, 79, 99
}
},
new PerInfo
{
Id = 3, Name = "小月", Age = 21, Scores = new List<int>()
{
95, 95, 96, 97
}
},
new PerInfo
{
Id = 4, Name = "小明", Age = 19, Scores = new List<int>()
{
96, 97, 98, 99
}
}
};
static void Main(string[] args)
{
Program p = new Program();
var query = from q in p.PerInfos
select q;
foreach (PerInfo per in query)
{
Console.WriteLine("姓名：{0}，年龄：{1}", per.Name, per.Age);
}
Console.ReadLine();
}
}
输出结果：
姓名：小白，年龄：15
姓名：小日，年龄：18
姓名：小月，年龄：21
姓名：小明，年龄：19
1.2 其他形式的select查询
class Program
{
public class PerInfo
{
public int Id
{
get;
set;
}
public string Name
{
get;
set;
}
public int Age
{
get;
set;
}
public List<int> Scores
{
get;
set;
}
public CustrInfo GetCustrInfo(List<CustrInfo> p, int id)
{
CustrInfo cInfo = (from q in p
where q.Id == id
select q).FirstOrDefault();
return cInfo;
}
public override string ToString()
{
return "姓名：" + Name + " 年龄：" + Age;
}
}
public class CustrInfo
{
public int Id
{
get;
set;
}
public string Tel
{
get;
set;
}
public string Email
{
get;
set;
}
public override string ToString()
{
return "邮箱：" + Email + "电话：" + Tel;
}
}
public class ScoreInfo
{
public double Average
{
get;
set;
}
public int ID
{
get;
set;
}
}
static void Main(string[] args)
{
List<PerInfo> perInfos = new List<PerInfo>()
{
new PerInfo
{
Id = 1, Name = "小白", Age = 15, Scores = new List<int>()
{
78, 88, 95, 60
}
},
new PerInfo
{
Id = 2, Name = "小日", Age = 18, Scores = new List<int>()
{
98, 86, 79, 99
}
},
new PerInfo
{
Id = 3, Name = "小月", Age = 21, Scores = new List<int>()
{
95, 95, 96, 97
}
},
new PerInfo
{
Id = 4, Name = "小明", Age = 19, Scores = new List<int>()
{
96, 97, 98, 99
}
}
};
List<CustrInfo> custrInfos = new List<CustrInfo>()
{
new CustrInfo {Id = 1, Tel = "110", Email = "Xuahau@123.Com"},
new CustrInfo {Id = 2, Tel = "120", Email = "xchads@qq.Com"},
new CustrInfo {Id = 3, Tel = "119", Email = "kashda@q56.Com"},
new CustrInfo {Id = 4, Tel = "999", Email = "sadhkuu@143.Com"}
};
Program p = new Program();
//1 根据查询条件查询数据源
var query1 = from q in perInfos
where q.Id > 1
select q;
Console.WriteLine("Query1:");
foreach (PerInfo per in query1)
{
Console.WriteLine(per.ToString());
}
//2 查询单个属性
var query2 = from q in perInfos
where q.Id > 1
select q.Name;
Console.WriteLine("\nQuery2:");
foreach (string s in query2)
{
Console.WriteLine(s);
}
//3 查询一个经过筛选的对象
var query3 = from q in perInfos
where q.Id > 1
select q.GetCustrInfo(custrInfos, q.Id);
Console.WriteLine("\nQuery3:");
foreach (CustrInfo c in query3)
{
Console.WriteLine(c.ToString());
}
//4 查询内部数组
var query4 = from q in perInfos
where q.Id > 1
select q.Scores[0];
Console.WriteLine("\nQuery4:");
foreach (int i in query4)
{
Console.WriteLine(i);
}
//5 表达式
var query5 = from q in perInfos
where q.Id > 1
select q.Scores[0] * 1.1;
Console.WriteLine("\nQuery5:");
foreach (int i in query5)
{
Console.WriteLine(i);
}
//6 求平均数
var query6 = from q in perInfos
where q.Id > 1
select q.Scores.Average();
Console.WriteLine("\nQuery6:");
foreach (int i in query6)
{
Console.WriteLine(i);
}
//7 查询多个属性
var query7 = from q in perInfos
where q.Id > 1
select new
{
q.Name, q.Age
};
Console.WriteLine("\nQuery7:");
foreach (var item in query7)
{
Console.WriteLine(item.Name + " " + item.Age);
}
//8 对查询结果进行投影
var query8 = from q in perInfos
where q.Id > 1
select new ScoreInfo
{
ID = q.Id,
Average = q.Scores.Average()
};
Console.WriteLine("\nQuery8:");
foreach (var item in query8)
{
Console.WriteLine("{0},{1}", item.ID, item.Average);
}
//9 查询平均分大于85的联系人信息
var query9 = from q in perInfos
where q.Scores.Average() > 85
join ci in custrInfos on q.Id equals ci.Id
select ci;
Console.WriteLine("\nQuery9:");
foreach (var item in query9)
{
Console.WriteLine("{0} {1} {2}", item.Id, item.Email, item.Tel);
}
Console.ReadLine();
}
}
输出结果：
Query1:
姓名：小日 年龄：18
姓名：小月 年龄：21
姓名：小明 年龄：19
Query2:
小日
小月
小明
Query3:
邮箱：xchads@qq.Com电话：120
邮箱：kashda@q56.Com电话：119
邮箱：sadhkuu@143.Com电话：999
Query4:
98
95
96
Query5:
107
104
105
Query6:
90
95
97
Query7:
小日 18
小月 21
小明 19
Query8:
2,90.5
3,95.75
4,97.5
Query9:
2 xchads@qq.Com 120
3 kashda@q56.Com 119
4 sadhkuu@143.Com 999
