详解在ASP.NET中用LINQ实现数据处理-c# linq groupby

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。

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