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Perform a save asynchronously

Last modified on September 17, 2012 16:10

You can perform an asynchronous save to help enhance the overall responsiveness of your application.


With the new task-based asynchronous programming model, an asynchronous save is as easy as a synchronous one.  

private async void DoSaveAsync() {
 try {
    await _manager.SaveChangesAsync();
 catch (EntityManagerSaveException) {
    MessageBox.Show("Save error");

Be sure to wrap your async call in a try/catch to handle the save errors which inevitably occur.  Or if you prefer, you can "try" a save and examine the save results:

private async void DoSaveAsync() {
  SaveResult saveResult = await _manager.TrySaveChangesAsync();
 if (!saveResult.Ok) {
     MessageBox.Show("save did not succeed");

You'll note we added the async (or Async in Visual Basic) modifier to indicate that the method contains asynchronous code, and the await (or Await) keyword to indicate that further processing in the method should be suspended until the asynchronous task completes. 

Since the entire entity cache will be saved during a call, there's no reason to issue multiple concurrent asynchronous saves from the same EntityManager.

Either a Task or Task<SaveResult> is returned from an async save.  The task represents the asynchronous operation, and will indicate the status of the operation, the results of a completed operation, and whether the operation was cancelled or failed.

Note that the task returned from a DevForce async method is "hot": it has already started and is scheduled for execution.

Cancelling a save

The asynchronous save task cannot itself be cancelled.  You can, however, cancel a save before it starts in an  EntityMaager Saving event handler.  You can also cancel the save in a custom EntityServerSaveInterceptor before the save begins on the server.  

In either case, the save task will be cancelled.  If you await the SaveChangesAsync call, an OperationCanceledException is thrown.  If you've called the TrySaveChangesAsync method, the SaveResult returned will indicate the save was cancelled.

Error handling

An awaited task will throw an exception if it's either faulted or cancelled.  This is why you should wrap any await calls in a try/catch.

Save processing exceptions are passed to the EntityManager's EntityServerError handler if one is defined.  If you do mark the error as handled the exception will not be rethrown.

Created by DevForce on February 19, 2011 23:55

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