知识大全 ADO.NET 2.0 数据异步处理改善用户体验

Posted 2022-07-18 知

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　　支持异步处理的提供程序有 System Data SqlClient在针对大批量数据插入过更新时使用异步处理方法可以不用等待多有数据更新完毕才能操作或者进行下步处理改善了用户体验 SqlCommand对象方法如下

　　异步方法 BeginExecuteNonQuery EndExecuteNonQuery BeginExecuteXmlReader EndExecuteXmlReader BeginExecuteReader EndExecuteReader begin前缀的方法传入参数 end前缀的方法返回输出参数和返回值 begin前缀方法返回的是IAsyncResult 用于追踪一步方法的执行状态 IAsyncResult AsnycState 用户自定义的状态对象 IAsyncResult AsnycWaitHandle 呼叫代码的等待形式是等其中的一个异步方法完成还是全部完成 IAsyncResult CompletedSynchronously 获取所有异步方法是否同时完成 IAsyncResult Ispleted 是否执行完毕可以根据此属性进行下部动作在连接字符串中加入 async＝true 如果所有的命令都是同步的建议在连接字符串中显施加入 async＝false 如果有一部分命令是异步执行又有一部分是同步同步执行建议分别建立两个连接对象如果 async＝true 时也可以执行同步命令但是会损失一些资源

　　/**///// obtain connection strings from configuration files or //// similar facility //// NOTE: these connection strings have to include async=true for //// example: //// server=myserver;database=mydb;integrated security=true;async=true //string connstrAccouting = GetConnString( accounting ); //string connstrHR = GetConnString( humanresources ); /**///// define o connection objects one for each database //using (SqlConnection connAcc = new SqlConnection(connstrAccounting)) //using (SqlConnection connHumanRes = new SqlConnection(connstrHR)) // // // open the first connection // connAcc Open(); // // start the execution of the first query contained in the // // employee_info stored procedure // SqlCommand cmdAcc = new SqlCommand( employee_info connAcc); // cmdAcc CommandType = CommandType StoredProcedure; // cmdAcc Parameters AddWithValue( @empl_id employee_id); // IAsyncResult arAcc = cmdAcc BeginExecuteReader(); // // at this point the employee_info stored proc is executing on // // the server and this thread is running at the same time // // now open the second connection // connHumanRes Open(); // // start the execution of the second stored proc against // // the human resources server // SqlCommand cmdHumanRes = new SqlCommand( employee_hrinfo // connHumanRes); // cmdHumanRes Parameters AddWithValue( @empl_id employee_id); // IAsyncResult arHumanRes = cmdHumanRes BeginExecuteReader(); // // now both queries are running at the same time // // at this point; more work can be done from this thread or we // // can simply wait until both mands finish in our case we ll // // wait // SqlDataReader drAcc = cmdAcc EndExecuteReader(arAcc); // SqlDataReader drHumanRes = cmdHumanRes EndExecuteReader(arHumanRes); // // now we can render the results for example bind the readers to an ASP NET // // web control or scan the reader and draw the information in a // // WebForms form //

　　string custid = ALFKI ; string orderid = ;

　　// NOTE: connection strings denoted by connstring have to include // async=true for example: string connstring = server=(local);database=northwind;integrated security=true;async=true ; // we ll use three connections for this using (SqlConnection c = new SqlConnection(connstring)) using (SqlConnection c = new SqlConnection(connstring)) using (SqlConnection c = new SqlConnection(connstring)) // get customer info c Open(); SqlCommand cmd = new SqlCommand( SELECT CustomerID CompanyName ContactName FROM Customers WHERE CustomerID=@id c ); cmd Parameters Add( @id SqlDbType Char ) Value = custid; IAsyncResult arCustomer = cmd BeginExecuteReader(); // get orders c Open(); SqlCommand cmd = new SqlCommand( SELECT * FROM Orders WHERE CustomerID=@id c ); cmd Parameters Add( @id SqlDbType Char ) Value = custid; IAsyncResult arOrders = cmd BeginExecuteReader(); // get order detail if user picked an order IAsyncResult arDetails = null; SqlCommand cmd = null; if (null != orderid) c Open(); cmd = new SqlCommand( SELECT * FROM [Order Details] WHERE OrderID=@id c ); cmd Parameters Add( @id SqlDbType Int) Value = int Parse(orderid); arDetails = cmd BeginExecuteReader(); // build the wait handle array for WaitForMultipleObjects WaitHandle[] handles = new WaitHandle[null == arDetails ? : ]; handles[ ] = arCustomer AsyncWaitHandle; handles[ ] = arOrders AsyncWaitHandle; if (null != arDetails) handles[ ] = arDetails AsyncWaitHandle; // wait for mands to plete and render page controls as we // get data back SqlDataReader r; DataTable dt; for (int results = (null == arDetails) ? : ; results < ; results++) // wait for any handle then process results as they e int index = WaitHandle WaitAny(handles false); // secs if (WaitHandle WaitTimeout == index) throw new Exception( Timeout ); switch (index) case : // customer query is ready r = cmd EndExecuteReader(arCustomer); if (!r Read()) continue; lblCustomerID Text = r GetString( ); lblCompanyName Text = r GetString( ); lblContact Text = r GetString( ); r Close(); break; case : // orders query is ready r = cmd EndExecuteReader(arOrders); dt = new DataTable(); dt Load(r); dgOrders DataSource = dt; // data bind to the orders grid dgOrders Refresh(); r Close(); break; case : // details query is ready r = cmd EndExecuteReader(arDetails); dt = new DataTable(); dt Load(r); dgDetails DataSource = dt; // data bind to the details grid dgDetails Refresh(); r Close(); break;

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