InvalidOperationException: open DataReader ...

InvalidOperationException: open DataReader ...

• Nikolaus Brennig

  Miha,

  Indeed, why not show you some code.

  The offending line of code is in assigning a reflected Table<T> to a ListBox.ItemsSource. The assignment is made prior to displaying a Page. Removing the Table<T> assignment removes the exceptional behavior seen during the 'Save' button click handler.

  ...

  // used when setting up gui controls

  Type[] types = { enumerationType };

  Type targetType = typeof(Table<>).MakeGenericType(types);

  // get the table containing the enumeration entityType in model

  FieldInfo[] fields = this.Model.GetType().GetFields();

  foreach (FieldInfo fiCandidate in fields)

  {

  if (fiCandidate.FieldType == targetType)

  {

  object oEnumerable = fiCandidate.GetValue(this.Model);

  // When the next line is commented the exception disappears

  //listBox.ItemsSource = (IEnumerable)oEnumerable;

  listBox.ItemTemplate = listBoxDataTemplate;

  break;

  }

  }

  ...

  // The event handler

  void m_btnSave_Click(object sender, RoutedEventArgs e)

  {

  try

  {

  // added new entity to DLinq DataContext

  if (m_bIsNewEntity)

  {

  Type[] types = { m_Type };

  Type targetType = typeof(Table<>).MakeGenericType(types);

  // get the table field

  FieldInfo[] fields = this.Model.GetType().GetFields();

  foreach (FieldInfo fiCandidate in fields)

  {

  if (fiCandidate.FieldType == targetType)

  {

  object oGenericTable = fiCandidate.GetValue(this.Model);

  MethodInfo miAdd = targetType.GetMethod("Add");

  object[] oEntityParameter = new object[] { this.Entity };

  // add the entity to the DataContext Table

  miAdd.Invoke(oGenericTable, oEntityParameter);

  break;

  }

  }

  }

  // save changes

  this.Model.SubmitChanges();

  // Raise EntitySaved event

  this.OnEntitySaved(m_oEntity);

  }

  catch (Exception ex)

  {

  this.Model.RejectChanges();

  }

  }

  Is listBox.ItemsSource simply being assigned improperly

  Cheers,

  Rana

  
  

• Chrisww2

  Thank You
  

• Tom ODonnell

  There aren't any open DataReaders, DataSets, instances of DataReaders or instances of DataSets. Only DLinq is used.

  The database table which is queried for the ListBox.ItemsSource does not have any data in it. Possibly DLinq maintains an open reader until some data is returned

  
  

• JohnEwing

  Do you have another open database reader elsewhere in your application If so, you must close that reader first. Even if your database is configured for MARS (multiple active result sets), it is not enabled by default, and is not currently supported by DLinq.

  
  
  

• synthkid

  Ok - I've confirmed that this is a bug in our connection management. Below is a simple repro for the issue. The workaround in your case is to buffer the data you are assigning to ListBox.ItemsSource (as seen in the ToArray() call below). Whats happening is that when ListBox executes the query by iterating over the items, it opens a reader on the database. Later, SubmitChanges also attempts to open a reader on the connection (to retrieve database properties); normally our connection management forces any other open readers to buffer, but it isn't working in this case. I'll log a bug

  Northwind db = new Northwind("Server=<yourserver>");

  IEnumerable<Customer> enumerable = db.Customers;
  IEnumerator<Customer> enumerator = enumerable.GetEnumerator();

  // Use this instead as workaround
  //IEnumerable<Customer> enumerable = db.Customers.ToArray();

  Customer newCust = new Customer();
  newCust.CustomerID = "ABCD";
  newCust.CompanyName = "EFGH";
  db.Customers.Add(newCust);
  db.SubmitChanges();
  

  
  
  

• markybark

  Can you show us some code
  
  
• InvalidOperationException: open DataReader ...