http://developer.51cto.com 2009-04-09 14:42 GWPBrian.net cnblogs
我要评论()个人认为学习LINQ法就是通过实例来学习。光看书本上的理论效率是很慢的。我将作一个简单的web应用程序，实现对数据的增删改操作。用到大家都熟悉的Northwind数据库。
一.引用命名空间
System.Data.Linq
System.Data.Linq.Mapping （需要在项目中先引用System.Data.Linq）
二.为数据库表创建实体类
Table(Name="Employees")]
public class Employee
{
[Column(IsDbGenerated=true,IsPrimaryKey=true)]
public int EmployeeID { get; set; }
[Column(Name="FirstName",DbType="varchar(20)")]
public string FirstName { get; set; }
[Column(Name = "LastName", DbType = "varchar(20)")]
public string LastName { get; set; }
}
常用的属性声明，可以很好的描述表中字段的属性：
Name: 字段的名称
DbType: 字段的数据类型
IsDbGenerated: 是否自动生成
CanBeNull: 字段是否为空
Storage: 保存数据的类字段名
三.创建一个强类型的数据环境
我们的数据库系统可能会和多种类型的数据源打交道，所以应该使我们的程序有和数据源进行创建连接的能力。这里我们将创建的NorthwindDb类继承DataContext基类。DataContext类表示LINQ to SQL 框架的主入口点。
其中有相关的处理LINQ to SQL的类，方法等。
public class NorthwindDb:DataContext
{
public NorthwindDb(string connectionString):base(connectionString)
{
}
public Table Employee;
}
四.创建Web From
首先为GridView绑定数据
private void BindGridView(string criteria)
{
string strConn = ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;
NorthwindDb db = new NorthwindDb(strConn);
IEnumerable results;
if (criteria == string.Empty)
{
results=db.Employee.ToArray();
}
else
{
results = (from c in db.Employee
where c.FirstName.Contains(criteria)
select c).ToArray();
}
GridView1.DataSource = results;
GridView1.DataBind();
}
搜索按钮只需将参数传进去即可BindGridView(TextBox1.Text);
如果选中了GridView中的某一行，则需要将选中的数据绑定到DetailsView 中进行编辑使用。
private void BindDetailsView()
{
int employeeID = (int)GridView1.SelectedValue;
string strConn = ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;
NorthwindDb db = new NorthwindDb(strConn);
var results = from emp in db.Employee
where emp.EmployeeID == employeeID
select emp;
DetailsView1.DataSource = results;
DetailsView1.DataBind();
}
protected void GridView1_SelectedIndexChanging(object sender, GridViewSelectEventArgs e)
{
GridView1.SelectedIndex = e.NewSelectedIndex;
}
protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{
int employeeID = (int)GridView1.SelectedValue;
string strConn = ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;
BindDetailsView();
}
接下来就是对数据的增删改操作：
protected void DetailsView1_ItemUpdating(object sender, DetailsViewUpdateEventArgs e)
{
string strConn = ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;
NorthwindDb db = new NorthwindDb(strConn);
var results = from emp in db.Employee
where emp.EmployeeID == (int)DetailsView1.SelectedValue
select emp;
results.First().FirstName = ((TextBox)DetailsView1.Rows[1].Cells[1].Controls[0]).Text;
results.First().LastName = ((TextBox)DetailsView1.Rows[2].Cells[1].Controls[0]).Text;
db.SubmitChanges();
BindGridView(string.Empty);
}
protected void DetailsView1_ItemInserting(object sender, DetailsViewInsertEventArgs e)
{
string strConn = ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;
NorthwindDb db = new NorthwindDb(strConn);
Employee emp = new Employee();
emp.FirstName = ((TextBox)DetailsView1.Rows[1].Cells[1].Controls[0]).Text;
emp.LastName= ((TextBox)DetailsView1.Rows[2].Cells[1].Controls[0]).Text;
db.Employee.InsertOnSubmit(emp);
db.SubmitChanges();
BindGridView(string.Empty);
}
protected void DetailsView1_ItemDeleting(object sender, DetailsViewDeleteEventArgs e)
{
string strConn = ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;
NorthwindDb db = new NorthwindDb(strConn);
var results = db.Employee.Single(emp => emp.EmployeeID==(int)DetailsView1.SelectedValue);
db.Employee.DeleteOnSubmit(results);
db.SubmitChanges();
BindGridView(string.Empty);
}
更新和添加的操作差不多，只是作了些小的改动。
ok，这就是在ASP.NET中利用LINQ对数据的操作。
