linq to sql简单使用

1.新建一个winform项目。

2.添加一个Linq to Sql 类，命名为Northwind



3.打开服务器资源管理器，将表拖动到linq to sql 类，实体类就由Vs生成了



4.实例化DataContext类

class="brush:csharp;gutter:true;">NorthwindDataContext dc = new NorthwindDataContext();

5.下面就可以使用Linq to Sql啦。

a.查询Employees所有数据

var ee =
from employee in dc.Employees
select employee;

b.加个Where条件，查询Employee表所有City=London

var e2 =
from employee in dc.Employees
where employee.City == "London"
select employee;

c.查询EmployeeID<5的数据

var e3 =
from employee in dc.Employees
where employee.EmployeeID < 5
select employee;

d.查询雇佣日期在1993年1月1日以前的人员。

var e4 =
from employee in dc.Employees
where employee.HireDate < new DateTime(1993, 1, 1)
select employee;

e.多个查询条件

var e5 =
from employee in dc.Employees
where employee.HireDate < new DateTime(1993, 1, 1)
where employee.EmployeeID < 3
select employee;

f.like语句

var e6 =
from employee in dc.Employees
where SqlMethods.Like(employee.FirstName, "%a%")
//where employee.FirstName.Contains("a")    //等价于 like '%a%'
//where employee.FirstName.StartsWith("a")  //等价于 like 'a%'
//where employee.FirstName.EndsWith("a")    //等价于 like '%a'
select employee;

g.查询指定的列

var e7 =
(from employee in dc.Employees
//select new { employee.EmployeeID, employee.FirstName };
select new
{
员工编号 = employee.EmployeeID,
员工姓名 = employee.FirstName,
尊称 = employee.TitleOfCourtesy
});

h.子查询

var e8 =
from employee in dc.Employees
where employee.Orders.Count > 100
select employee;

i.内连接

/**
* 查询位于伦敦的客户的订单
* SELECT *
* FROM [dbo].[Orders]
* INNER JOIN [dbo].[Customers] ON [Customers].[CustomerID] = [Orders].[CustomerID]
* WHERE [Customers].[City] = 'London'
*/
var e9 =
from cus in dc.Customers
join ord in dc.Orders on cus.CustomerID equals ord.CustomerID
where cus.City == "London"
select ord;

j.增加

Employees m = new Employees();
m.LastName = "闪硕";
m.FirstName = "燕";
m.Title = "闪硕标题";
dc.Employees.InsertOnSubmit(m);
dc.SubmitChanges();

k.修改

var e10 = dc.Employees.FirstOrDefault(employee => employee.LastName == "闪硕");
e10.City = "石家庄";
dc.SubmitChanges();

l.删除

var e10 = dc.Employees.FirstOrDefault(employee => employee.LastName == "闪硕");
dc.Employees.DeleteOnSubmit(e10);
dc.SubmitChanges();