代码分析ADO.NET数据异步处理-postgresql数据库内核分析

#T#很多开发语言都支持异步通信，在ADO.NET中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ADO.NET数据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：

ADO.NET数据异步处理
◆BeginExecuteNonQueryEndExecuteNonQuery
◆BeginExecuteXmlReaderEndExecuteXmlReader
◆BeginExecuteReaderEndExecuteReader
◆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.Iscompleted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

/**/////obtainconnectionstringsfromconfigurationfilesor  
////similarfacility  
////NOTE:theseconnectionstringshavetoinclude"async=true",for  
////example:  
////"server=myserver;database=mydb;integratedsecurity=true;async=true"  
//stringconnstrAccouting=GetConnString("accounting");  
//stringconnstrHR=GetConnString("humanresources");  
/**/////definetwoconnectionobjects,oneforeachdatabase  
//using(SqlConnectionconnAcc=newSqlConnection(connstrAccounting))  
//using(SqlConnectionconnHumanRes=newSqlConnection(connstrHR))  
//{  
////openthefirstconnection  
//connAcc.Open();  
////starttheexecutionofthefirstquerycontainedinthe  
////"employee_info"stored-procedure  
//SqlCommandcmdAcc=newSqlCommand("employee_info",connAcc);  
//cmdAcc.CommandType=CommandType.StoredProcedure;  
//cmdAcc.Parameters.AddWithValue("@empl_id",employee_id);  
//IAsyncResultarAcc=cmdAcc.BeginExecuteReader();  
////atthispoint,the"employee_info"stored-procisexecutingon  
////theserver,andthisthreadisrunningatthesametime  
////nowopenthesecondconnection  
//connHumanRes.Open();  
////starttheexecutionofthesecondstored-procagainst  
////thehuman-resourcesserver  
//SqlCommandcmdHumanRes=newSqlCommand("employee_hrinfo",  
//connHumanRes);  
//cmdHumanRes.Parameters.AddWithValue("@empl_id",employee_id);  
//IAsyncResultarHumanRes=cmdHumanRes.BeginExecuteReader();  
////nowbothqueriesarerunningatthesametime  
////atthispoint;moreworkcanbedonefromthisthread,orwe  
////cansimplywaituntilbothcommandsfinish-inourcasewe'll  
////wait  
//SqlDataReaderdrAcc=cmdAcc.EndExecuteReader(arAcc);  
//SqlDataReaderdrHumanRes=cmdHumanRes.EndExecuteReader(arHumanRes);  
////nowwecanrendertheresults,forexample,bindthereaderstoanASP.NET  
////webcontrol,orscanthereaderanddrawtheinformationina  
////WebFormsform.  
//}  
 
stringcustid="ALFKI";  
stringorderid="10643";  
 
//NOTE:connectionstringsdenotedby"connstring"havetoinclude  
//"async=true",forexample:  
stringconnstring="server=(local);database=northwind;integratedsecurity=true;async=true";  
//we'llusethreeconnectionsforthis  
using(SqlConnectionc1=newSqlConnection(connstring))  
using(SqlConnectionc2=newSqlConnection(connstring))  
using(SqlConnectionc3=newSqlConnection(connstring))  
{  
//getcustomerinfo  
c1.Open();  
SqlCommandcmd1=newSqlCommand(  
"SELECTCustomerID,CompanyName,ContactNameFROMCustomersWHERECustomerID=@id",c1);  
cmd1.Parameters.Add("@id",SqlDbType.Char,5).Value=custid;  
IAsyncResultarCustomer=cmd1.BeginExecuteReader();  
//getorders  
c2.Open();  
SqlCommandcmd2=newSqlCommand("SELECT*FROMOrdersWHERECustomerID=@id",c2);  
cmd2.Parameters.Add("@id",SqlDbType.Char,5).Value=custid;  
IAsyncResultarOrders=cmd2.BeginExecuteReader();  
//getorderdetailifuserpickedanorder  
IAsyncResultarDetails=null;  
SqlCommandcmd3=null;  
if(null!=orderid)  
{  
c3.Open();  
cmd3=newSqlCommand("SELECT*FROM[OrderDetails]WHEREOrderID=@id",c3);  
cmd3.Parameters.Add("@id",SqlDbType.Int).Value=int.Parse(orderid);  
arDetails=cmd3.BeginExecuteReader();  
}  
//buildthewaithandlearrayforWaitForMultipleObjects  
WaitHandle[]handles=newWaitHandle[null==arDetails?2:3];  
handles[0]=arCustomer.AsyncWaitHandle;  
handles[1]=arOrders.AsyncWaitHandle;  
if(null!=arDetails)  
handles[2]=arDetails.AsyncWaitHandle;  
//waitforcommandstocompleteandrenderpagecontrolsaswe  
//getdataback  
SqlDataReaderr;  
DataTabledt;  
for(intresults=(null==arDetails)?1:0;results<3;results++)  
{  
//waitforanyhandle,thenprocessresultsastheycome  
intindex=WaitHandle.WaitAny(handles,5000,false);//5secs  
if(WaitHandle.WaitTimeout==index)  
thrownewException("Timeout");  
switch(index)  
{  
case0://customerqueryisready  
r=cmd1.EndExecuteReader(arCustomer);  
if(!r.Read())  
continue;  
lblCustomerID.Text=r.GetString(0);  
lblCompanyName.Text=r.GetString(1);  
lblContact.Text=r.GetString(2);  
r.Close();  
break;  
case1://ordersqueryisready  
r=cmd2.EndExecuteReader(arOrders);  
dt=newDataTable();  
dt.Load(r);  
dgOrders.DataSource=dt;//data-bindtotheordersgrid  
dgOrders.Refresh();  
r.Close();  
break;  
case2://detailsqueryisready  
r=cmd3.EndExecuteReader(arDetails);  
dt=newDataTable();  
dt.Load(r);  
dgDetails.DataSource=dt;//data-bindtothedetailsgrid  
dgDetails.Refresh();  
r.Close();  
break;  
 
}  
}  
}

以上就是ADO.NET数据异步处理用户体验的一个解决方案，大家快试试。