SqlDataReader错误

Question

我试图使SqlParameter和当我运行网站错误出现在SqlDataReader _dataReader = _command.ExecuteReader();中

这是我的代码：

private void goLogin()
{
   conn.ConnectionString = _connectionString;
   conn.Open();
   string username = txt_username.Text;
   _sqlCodes = "SELECT ACC_PASS,ACC_ID" +
   "FROM ACC WHERE ACC_USER = @username";
   SqlCommand _command = new SqlCommand(_sqlCodes);
   _command.Parameters.Add(new SqlParameter("@username",username));
   SqlDataReader _dataReader = _command.ExecuteReader();

   //more codes here...
   conn.Close();
}

错误：

“/”应用程序.中的服务器错误

ExecuteReader:连接属性尚未初始化。

描述：是在执行当前web请求时发生的一个未处理的异常。请查看堆栈跟踪以获得有关错误的更多信息，以及它起源于代码的位置。

异常详细信息： System.InvalidOperationException: ExecuteReader: Connection属性尚未初始化。

源错误：

Line 31:             SqlCommand _command = new SqlCommand(_sqlCodes);
Line 32:             _command.Parameters.Add(new SqlParameter("username",username));
Line 33:             SqlDataReader _dataReader = _command.ExecuteReader();
Line 34:             conn.Close();
Line 35:         }

源文件： C:\Users\arnie.mateo\Desktop\GoWireless Project Leonel\GoWireless\GoWireless\account.aspx.cs Line: 33

堆栈跟踪：

[InvalidOperationException: ExecuteReader: Connection property has not been initialized.]
System.Data.SqlClient.SqlCommand.ValidateCommand(String method, Boolean async) +5089605
System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) +87
System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method) +32
System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method) +141
System.Data.SqlClient.SqlCommand.ExecuteReader() +89
GoWireless.WebForm1.goLogin() in C:\Users\arnie.mateo\Desktop\GoWireless Project Leonel\GoWireless\GoWireless\account.aspx.cs:33
GoWireless.WebForm1.btn_login_Click(Object sender, EventArgs e) in C:\Users\arnie.mateo\Desktop\GoWireless Project Leonel\GoWireless\GoWireless\account.aspx.cs:52
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +118
System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +112
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5563

版本信息：微软.NET框架版本:4.0.30319；ASP.NET版本:4.0.30319.272

Answer 1

您必须给出SqlCommand的连接名。

使用SqlCommand _command = new SqlCommand(_sqlCodes, conn);

Answer 2

SqlCommand对象不知道要使用哪个连接。您可以使用以下方法创建命令：

SqlCommand _command = conn.CreateCommand();

或在其上设置连接：

_command.Connection = conn;