MySql 데이터베이스에서 작동해야하는 응용 프로그램을 만들고 있습니다. 이유를 알고 나는이 오류를 얻고있다, 나는 그나마 내 테이블 중 하나에서 열 "priemer"가있는 경우개체 참조가 개체의 인스턴스로 설정되지 않았습니다. - MySqlCommand
public void rtMean()
{
MySqlConnection conect = con.ConnectToMySQL();
MySqlDataReader reader;
MySqlDataReader readerMean;
// OVERENIE, CI UZ STLPEC PRIEMER EXISTUJE
string query1 = "SELECT * FROM feture";
MySqlCommand cmd1 = new MySqlCommand(query1, conect);
reader = cmd1.ExecuteReader();
for (int j=0; j < reader.FieldCount; j++)
{
if (reader.GetName(j) == "priemer")
{
break;
}
else
{
reader.Close();
cmd1.Cancel();
string queryAlterTable = "ALTER TABLE feture ADD COLUMN priemer FLOAT NOT NULL";
MySqlCommand cmd = new MySqlCommand(queryAlterTable, conect); //here I am getting the error
cmd.ExecuteScalar();
}
}
이 chceck해야
Object reference not set to an instance of an object
가 여기 내 코드입니다. 예이면 끝나야하고, 없으면 내 테이블을 "priemer"라는 새 열로 변경해야합니다.
감사합니다.
편집 : STACK - TRACE : 내가 제대로 이해한다면 첫 번째 필드의 이름되지 않은 경우
at MySql.Data.MySqlClient.MySqlCommand.ExecuteScalar()
at WindowsFormsApplication1.ClusteringReady.rtMean() in c:\Users\Martin\Desktop\CLUSTER\WindowsFormsApplication1\ClusteringReady.cs:line 43
at WindowsFormsApplication1.Form1.clusterize_Click(Object sender, EventArgs e) in c:\Users\Martin\Desktop\CLUSTER\WindowsFormsApplication1\Form1.cs:line 130
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.Run(Form mainForm)
at WindowsFormsApplication1.Program.Main() in c:\Users\Martin\Desktop\CLUSTER\WindowsFormsApplication1\Program.cs:line 19
at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
예외의 스택 추적은 무엇입니까? – adrianbanks
@adrianbanks 제 편집을 확인해주세요. –