获取错误 "Object Reference not set to an instance of an object" Linq to SQL Database Insret a XML file As VarBinary

Question

我遇到错误

Object Reference not set to an instance of an object

public static void SaveDashboardStream(string connectionString, MemoryStream ms)
{
  using (DashboardDBConDataContext db = new DashboardDBConDataContext(connectionString))
   {
     DBDashboard storedDashboard = (from t in db.Dashboards
                                               select t).FirstOrDefault();
     ms.Seek(0, SeekOrigin.Begin);
     storedDashboard.DashboardStream = new Binary(ms.ToArray());
     db.SubmitChanges();
  }
}

我在函数中使用上面的代码 As

private void DashBoardGenerator_DashboardSaving(object sender, DashboardSavingEventArgs e)
{
  // Determines whether the user has called the Save command.
  if (e.Command == DashboardSaveCommand.Save) 
  {
     try
     {
       using (MemoryStream saveStream = new MemoryStream())
       {
         Dashboard.SaveToXml(saveStream);
         DashboardSql.SaveDashboardStream(dashboardStorageConnectionString, saveStream);
       }
       e.Handled = true;
     }
     catch (Exception ex)
     {
      XtraMessageBox.Show(ex.Message, "Unable to Save Dashboard", MessageBoxButtons.OK, MessageBoxIcon.Error);
     }
  } 
}

如果我哪里错了请指导？

Answer 1

可能storedDashboard似乎是空的。

using (DashboardDBConDataContext db = new DashboardDBConDataContext(connectionString))
{
     DBDashboard storedDashboard = (from t in db.Dashboards
                                    select t).FirstOrDefault();

     //Always check for null when selecting First() or FirstOrDefault()
     if(storedDashboard == null) {
        storedDashboard = new DBDashboard();
     }

     ms.Seek(0, SeekOrigin.Begin);
     storedDashboard.DashboardStream = new Binary(ms.ToArray());
     db.SubmitChanges();
}