美好的一天.
请帮助我使用Generic Lists如何使用sqlCommand类的三个方法BeginExecuteReader().我使用BeginExecuteReader创建了一个方法,但我不知道这是否是最好的使用方法
public class Empresa {
public Empresa() {
PkEmpresa = -1;
CodigoEmpresa = "";
Descripcion = "";
PkCategoriaEmpresa = -1;
}
public int PkEmpresa { get; set; }
public string CodigoEmpresa { get; set; }
public string Descripcion { get; set; }
public int PkCategoriaEmpresa { get; set; }
public Empresa ShallowCopy() {
return (Empresa)this.MemberwiseClone();
}
}
public class AsyncronousDAL {
private static string getConexion() {
return "Data Source=DATABASE;Initial Catalog=DATA_BASE;Integrated Security=True;Asynchronous Processing=True";
}
public static List<Empresa> ConsultaAsincrona() {
List<Empresa> _resultados = new List<Empresa>();
using (sqlConnection conexion = new sqlConnection(getConexion())) {
using (sqlCommand commando = new sqlCommand("[dbo].[pruebaAsync]",conexion)) {
commando.CommandType = System.Data.CommandType.StoredProcedure;
conexion.Open();
IAsyncResult resultado = commando.BeginExecuteReader();
using (sqlDataReader reader = commando.EndExecuteReader(resultado)) {
while (reader.Read()) {
_resultados.Add(new Empresa() {
PkEmpresa = Convert.ToInt32(reader["PkEmpresa"]),CodigoEmpresa = reader["CodigoEmpresa"].ToString(),Descripcion = reader["Descripcion"].ToString(),PkCategoriaEmpresa = Convert.ToInt32(reader["PkCategoriaEmpresa"])
});
}
}
}
}
return _resultados;
}
}
解决方法
如果您不熟悉Asynch模式,那么Web上有很多教程和示例.这是旧的,但仍然相关：
http://msdn.microsoft.com/en-us/library/aa719595(v=vs.71).aspx
当您调用BeginExecuteReader时,工作将最终被推送到工作线程,允许您的main继续执行.当您调用EndExecuteReader时,将导致主线程阻塞,直到该任务完成.
如果您立即调用EndExecuteReader – 您实际上并没有获得任何好处(事实上,您正在引入额外的开销).
看一下这里的例子：http://msdn.microsoft.com/en-us/library/7szdt0kc.aspx
The BeginExecuteReader method returns immediately,but until the code
executes the corresponding EndExecuteReader method call,it must not
execute any other calls that start a synchronous or asynchronous
execution against the same sqlCommand object. Calling the
EndExecuteReader before the command’s execution is completed cause the
sqlCommand object to block until the execution is finished.
这是代码的相关部分：
// Although it is not required that you pass the // sqlCommand object as the second parameter in the // BeginExecuteReader call,doing so makes it easier // to call EndExecuteReader in the callback procedure. AsyncCallback callback = new AsyncCallback(HandleCallback); command.BeginExecuteReader(callback,command);