linqtosql簡(jiǎn)單使用

2019-11-14 16:44:50

字體：大中小

供稿：網(wǎng)友

1.新建一個(gè)winform項(xiàng)目。

2.添加一個(gè)Linq to Sql 類，命名為Northwind

3.打開服務(wù)器資源管理器，將表拖動(dòng)到linq to sql 類，實(shí)體類就由Vs生成了

4.實(shí)例化DataContext類

NorthwindDataContext dc = new NorthwindDataContext();

5.下面就可以使用Linq to Sql啦。

a.查詢Employees所有數(shù)據(jù)

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

b.加個(gè)Where條件，查詢Employee表所有City=London

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

c.查詢EmployeeID<5的數(shù)據(jù)

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

d.查詢雇傭日期在1993年1月1日以前的人員。

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

e.多個(gè)查詢條件

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

f.like語句

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

g.查詢指定的列

           var e7 =                (from employee in dc.Employees                 //select new { employee.EmployeeID, employee.FirstName };                 select new                 {                     員工編號(hào) = employee.EmployeeID,                     員工姓名 = employee.FirstName,                     尊稱 = employee.TitleOfCourtesy                 });

h.子查詢

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

i.內(nèi)連接

            /**             * 查詢位于倫敦的客戶的訂單             * 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 = "閃碩";            m.FirstName = "燕";            m.Title = "閃碩標(biāo)題";            dc.Employees.InsertOnSubmit(m);            dc.SubmitChanges();

k.修改

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

l.刪除

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

練習(xí)代碼使用Vs2012，微軟northwnd示例數(shù)據(jù)庫

代碼下載：http://pan.baidu.com/s/1pJyh0Mn　　

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