DataAdapter对象

DataAdapter对象用于从数据源中获取数据，填充DataSet中的表和约束，并将对DataSet的更改提交回数据源。
DataAdapter对象有4个重要属性，即SelectCommand、InsertCommand、UpdateCommand和DeleteCommand，这四个属性都是Command对象。

protected   void  Page_Load( object  sender, EventArgs e)
    {
        OleDbConnection conn  =   new  OleDbConnection();
        conn.ConnectionString  =   " Provider=Microsoft.Jet.OLEDB.4.0; "   +
             " Data Source= "   +  Server.MapPath( " person.mdb " );
        conn.Open();
         string  sql = " select * from grade " ;
        OleDbDataAdapter da  =   new  OleDbDataAdapter(sql, conn);
        DataSet ds  =   new  DataSet();
        da.Fill(ds,  " grade " );
        dg.DataSource  =  ds.Tables[ " grade " ].DefaultView;
        dg.DataBind();
        conn.Close();
    }

通过DataAdapter对象的构造函数"OleDbDataAdapter(sql, conn)"，传入数据库连接对象和SQL语句，如果要处理DataAdapter对象中的数据，需要将其传递给DataSet对象。语句"da.Fill(ds, "grade")"的功能是将da中的数据填充到DataSet对象中，并起一个别名"grade"。程序最后将DataSet对象中的数据和DataGrid进行绑定，然后输出。

DataAdapter对象还可以通过4个属性传递数据，给4个属性赋值的对象必须是Command对象。如果Command对象执行的是Select语句，必须将对象传递给SelectCommand属性；如果是Update语句，则传递给UpdateCommand属性；如果是Insert语句，则传递给InsertCommand属性；如果是Delete语句，则传递给DeleteCommand属性。

protected   void  Page_Load( object  sender, EventArgs e)
    {
        OleDbConnection conn  =   new  OleDbConnection();
        conn.ConnectionString  =   " Provider=Microsoft.Jet.OLEDB.4.0; "   +
             " Data Source= "   +  Server.MapPath( " person.mdb " );
         string  sql = " select * from grade " ;
        OleDbCommand Comm  =   new  OleDbCommand(sql, conn);
        OleDbDataAdapter da  =   new  OleDbDataAdapter();
        da.SelectCommand  =  Comm;
        conn.Open();
        DataSet ds  =   new  DataSet();
        da.Fill(ds,  " grade " );
        dg.DataSource  =  ds.Tables[ " grade " ].DefaultView;
        dg.DataBind();
        conn.Close();
    }

默认情况下，当Connection对象执行Open方法的时候，DataAdapter对象将自动调用SelectCommand属性。除了SelectCommand属性，其他3个属性都需要使用"ExecuteNonQuary()"方法调用。

protected   void  Page_Load( object  sender, EventArgs e)
    {
        OleDbConnection Conn  =   new  OleDbConnection();
        Conn.ConnectionString  =   " Provider=Microsoft.Jet.OLEDB.4.0; "   +
             " Data Source= "   +  Server.MapPath( " person.mdb " );
        Conn.Open();
         string  strInsertSQL  =   " insert into grade values(13,'女','小唐',98,78,88) " ;
         string  strSelectSQL = " select * from grade " ;
         string  strUpdateSQL  =   " update grade set 数学=60 where 学号=13 " ;
         string  strDeleteSQL  =   " delete from grade where 学号=13 " ;
         // 创建Command对象
        OleDbCommand InsertComm  =   new  OleDbCommand(strInsertSQL, Conn);
        OleDbCommand SelectComm  =   new  OleDbCommand(strSelectSQL, Conn);
        OleDbCommand UpdateComm  =   new  OleDbCommand(strUpdateSQL, Conn);
        OleDbCommand DeleteComm  =   new  OleDbCommand(strDeleteSQL, Conn);
         // 创建DataAdapter对象da
        OleDbDataAdapter da  =   new  OleDbDataAdapter();
        da.SelectCommand  =  SelectComm;
        da.InsertCommand  =  InsertComm;
        da.UpdateCommand  =  UpdateComm;
        da.DeleteCommand  =  DeleteComm;
         // 创建并填充DataSet
        DataSet ds  =   new  DataSet();
        da.Fill(ds,  " grade1 " );
        da.DeleteCommand.ExecuteNonQuery(); 
        da.Fill(ds,  " grade2 " );
        da.InsertCommand.ExecuteNonQuery();
        da.Fill(ds,  " grade3 " );
        da.UpdateCommand.ExecuteNonQuery();
        da.Fill(ds,  " grade4 " );
         // 将DataSet绑定到DataGrid控件
        dg1.DataSource  =  ds.Tables[ " grade1 " ].DefaultView;
        dg2.DataSource  =  ds.Tables[ " grade2 " ].DefaultView;
        dg3.DataSource  =  ds.Tables[ " grade3 " ].DefaultView;
        dg4.DataSource  =  ds.Tables[ " grade4 " ].DefaultView;
        dg1.DataBind();
        dg2.DataBind();
        dg3.DataBind();
        dg4.DataBind();
        Conn.Close();
    }