Linq复杂对象查询
复杂的查询对象，
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
var queryResults = from c in customers
where c.Region == "Asia"
select c;
Console.WriteLine("亚洲的有:");
foreach (Customer c in queryResults)
{
Console.WriteLine(c);
}
Console.ReadLine();
}
}
}
查询对象的某个元素
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
var queryResults = from c in customers
where c.Region == "Asia"
select c.City;
Console.WriteLine("亚洲的城市有:");
foreach (String city in queryResults)
{
Console.WriteLine(city);
}
Console.ReadLine();
}
}
}
查询结果只能是字符串，或者一个对象
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
var queryResults = from c in customers
where c.Region == "Asia"
select new { c.City, c.Country };
Console.WriteLine("亚洲的有:");
foreach (Object item in queryResults)
{
Console.WriteLine(item);
}
Console.ReadLine();
}
}
}
用Select函数
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
//var queryResults = from c in customers
// where c.Region == "Asia"
// select new { c.City, c.Country };
var queryResults = customers.Where(c => c.Region == "Asia").Select(c => new { c.City, c.Country });
Console.WriteLine("亚洲的有:");
foreach (Object item in queryResults)
{
Console.WriteLine(item);
}
Console.ReadLine();
}
}
}
去重处理Distinct方法
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
//var queryResults = from c in customers
// where c.Region == "Asia"
// select new { c.City, c.Country };
var queryResults = customers.Select(c => c.Region).Distinct();
Console.WriteLine("洲有:");
foreach (Object item in queryResults)
{
Console.WriteLine(item);
}
Console.ReadLine();
}
}
}
any，All查询
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
// Any All
bool anyUSA = customers.Any(c => c.Country == "USA");
if (anyUSA)
{
Console.WriteLine("有些人是美国的");
}
else
{
Console.WriteLine("没有美国的");
}
bool allAsia = customers.All(c => c.Region == "Asia");
if (allAsia)
{
Console.WriteLine("全是亚洲的人");
}
else
{
Console.WriteLine("不全是亚洲的人");
}
Console.ReadLine();
}
}
}
多级排序
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
var queryResults = from c in customers
orderby c.Region,c.Country,c.City // 多级排序
select new {c.Region , c.Country, c.City };
Console.WriteLine("亚洲的有:");
foreach (Object item in queryResults)
{
Console.WriteLine(item);
}
Console.ReadLine();
}
}
}
使用OrderBy，ThenBy实现
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
//var queryResults = from c in customers
// orderby c.Region,c.Country,c.City // 多级排序
// select new {c.Region , c.Country, c.City };
var queryResults = customers.OrderBy(c => c.Region)
.ThenBy(c => c.Country)
.ThenBy(c => c.City)
.Select(c => new { c.Region,c.Country, c.City});
Console.WriteLine("亚洲的有:");
foreach (Object item in queryResults)
{
Console.WriteLine(item);
}
Console.ReadLine();
}
}
}
group的使用
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
var queryResults = from c in customers
group c by c.Region into cg
select new { TotalSales = cg.Sum(c => c.Sales),Region = cg.Key };
var orderedResults =
from cg in queryResults
orderby cg.TotalSales descending
select cg;
foreach (var item in orderedResults)
{
Console.WriteLine(item.TotalSales+"\t:"+item.Region);
}
Console.ReadLine();
}
}
}
通过Take方法获取前几个数据
通过Skip方法，获取剩下的数据
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
var queryResults = from c in customers
group c by c.Region into cg
select new { TotalSales = cg.Sum(c => c.Sales),Region = cg.Key };
var orderedResults =
from cg in queryResults
orderby cg.TotalSales descending
select cg;
// Take获取前几个数据
// Skip获取后几个数据
// 出去前1个后的数据
foreach (var item in orderedResults.Skip(1))
{
Console.WriteLine(item.TotalSales + "\t:" + item.Region);
}
Console.WriteLine("----------------------------------------");
// 前1个
foreach (var item in orderedResults.Take(1))
{
Console.WriteLine(item.TotalSales + "\t:" + item.Region);
}
Console.ReadLine();
}
}
}
First与FirstOrDefault
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
var queryResults = from c in customers
group c by c.Region into cg
select new { TotalSales = cg.Sum(c => c.Sales),Region = cg.Key };
var orderedResults =
from cg in queryResults
orderby cg.TotalSales descending
select cg;
// 获取第一个数据,First和FirstOrDefault
// First方法如何数据不存在，会报错
Console.WriteLine(orderedResults.First());
Console.WriteLine(orderedResults.FirstOrDefault());
Console.WriteLine(orderedResults.First(c => c.Region == "Europe"));
Console.WriteLine(orderedResults.FirstOrDefault(c => c.Region == "Europe"));
Console.ReadLine();
}
}
}
JOIN使用
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace LinqDemo
{
class Customer
{
public string ID { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string Region { get; set; }
public decimal Sales { get; set; }
public override string ToString()
{
return "ID:" + ID + " City:" + City + " Country:" + Country + " Region:" + Region + " Sales:" + Sales;
}
}
class Order
{
public string ID { get; set; }
public decimal Amount { get; set; }
}
class Program
{
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>
{
new Customer {ID="A",City="New York",Country="USA",Region="North America",Sales=999 },
new Customer {ID="B",City="Bei Jing",Country="China",Region="Asia",Sales=1999 },
new Customer {ID="C",City="Shang Hai",Country="China",Region="Asia",Sales=9999 },
new Customer {ID="D",City="Tokyo",Country="Japan",Region="Asia",Sales=2999 },
new Customer {ID="E",City="London",Country="England",Region="Europe",Sales=3999 }
};
List<Order> orders = new List<Order>
{
new LinqDemo.Order {ID = "A",Amount = 100 },
new LinqDemo.Order {ID = "A",Amount = 200 },
new LinqDemo.Order {ID = "B",Amount = 300 },
new LinqDemo.Order {ID = "B",Amount = 400 },
new LinqDemo.Order {ID = "C",Amount = 500 },
new LinqDemo.Order {ID = "D",Amount = 600 },
};
var queryResults = from c in customers
join o in orders on c.ID equals o.ID
select new { c.ID,c.City,SalesBefore = c.Sales,NewOrder = o.Amount,SalesAfter = c.Sales + o.Amount };
foreach (var item in queryResults)
{
Console.WriteLine(item);
}
Console.ReadLine();
}
}
}
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