linqtosql简单使用

2019-11-14 16:44:50

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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

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();

练习代码使用Vs2012，微软northwnd示例数据库

代码下载：http://pan.baidu.com/s/1pJyh0Mn　　

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