I'm looking for some guidance on an situation I've been contemplating.
I'm creating an Async Crud Operations, and using the time during communication to validate, and only commit the transaction if this is valid.
public async Task<SkillDTO> Update(int id, SkillDTO skillDTO)
{
using (var transaction = this._context.Database.BeginTransaction())
{
var skill = await this._context.Skills.FindAsync(id);
skillDTO.CopyTo(new SkillAdapter(skill));
//Start SaveChanges Execution
var saveChangesTask = this._context.SaveChangesAsync();
//Use free time to validate
var validator = new SkillValidator();
//Note Validator Will throw if not valid
validator.Validate(skill);
await saveChangesTask;
transaction.Commit();
return new SkillAdapter(skill).ToDTO();
}
}
What the pro's and con's?
Is this a dangerous operation because you are executing code that is unneeded if failed validation?
Or does this seem like a valid way to increase efficiency?
Related
After much toil and trial and error I managed to issue a "request" from my saga and see it handle the response. My jubilation was cut short however by the appearance of a message in my states' skipped queue. (i'm using azure service bus)
It is of type "urn:message:MassTransit.Scheduling:CancelScheduledMessage".
I am a complete newbie at with mass transit and I'm just trying to get a contrived example going.
My saga calls TaxiToRunway/TaxiingComplete. My bit of saga code
Request(()=>TaxiToRunway, config =>
{
config.Timeout = TimeSpan.FromSeconds(30);
});
...
public Request<PlaneState, TaxiToRunway, TaxiingComplete> TaxiToRunway { get; private set; }
...
Initially(
When(ReadyToDepart)
.Then(context =>
{
context.Saga.Altitude = 0;
context.Saga.Speed = 0;
context.Saga.FlightNo = context.Message.FlightNo;
context.Saga.CorrelationId = context.Message.CorrelationId;
Console.WriteLine($"Flight {context.Message.FlightNo} is ready to depart.");
})
.TransitionTo(Taxiing)
.Request(TaxiToRunway,
(context) => context.Init<TaxiToRunway>(new {CorrelationId = context.Saga.CorrelationId}))
...
During(Taxiing,
Ignore(ReadyToDepart),
When(TaxiToRunway.Completed)
.Then(x =>
{
x.ToString();
})
.TransitionTo(TakingOff),
With a debugger attached I hit the x.ToString() line.
The consumer (in a different host):
public class TaxiToRunwayConsumer: IConsumer<TaxiToRunway>
{
public async Task Consume(ConsumeContext<TaxiToRunway> context)
{
await context.RespondAsync<TaxiingComplete>(new
{
context.Message.CorrelationId
});
}
}
Saga startup config:
cfg.AddSagaStateMachine<PlaneStateMachine, PlaneState>()
.MessageSessionRepository();
cfg.AddServiceBusMessageScheduler();
cfg.UsingAzureServiceBus((context, sbCfg) =>
{
var connectionString = appConfig.ServiceBus.ConnectionString;
sbCfg.Host(connectionString);
EndpointConvention.Map<TaxiToRunway>(new Uri("sb://xxx.servicebus.windows.net/taxi-to-runway"));
sbCfg.UseServiceBusMessageScheduler();
sbCfg.ReceiveEndpoint("plane-state", e =>
{
e.UseInMemoryOutbox();
e.RequiresSession = true;
e.PrefetchCount = 50;
e.MaxConcurrentCalls = 50;
e.ConfigureSaga<PlaneState>(context);
});
sbCfg.ConfigureEndpoints(context);
});
I can see this in the log output:
dbug: MassTransit.Messages[0]
SEND sb://dbpdf-us-dev-sam.servicebus.windows.net/plane-state 80d90000-5d7b-2cf0-7a6b-08da0fd3e7b7 MassTransit.Scheduling.CancelScheduledMessage
Am I supposed to be handling this as an event??
Learning curve on this sure is steep! My question is what do I need to do to not have these messages go to skipped?
So, the reason this doesn't work:
The message session saga repository can only correlate by the SessionId, since it's session-stored data.
The requestId, therefore, MUST equal the saga instance correlationId (aka, the SessionId)
The timeout message, sent by the request, gets a tokenId based upon the sequence number of the scheduled message
Which isn't saved anywhere
So the request timeout isn't canceled
The proper approach, in this scenario, is to use a Request/Response that doesn't have a timeout and use a separate Schedule to schedule the timeout yourself.
I have an async member which ultimately needs to invoke some UI updates, after getting some data from a server.
I think I need something like BeginInvokeOnMainThread, or Dispatcher.Invoke, but neither of these appear to be recognized in the Uno context.
Here's the essence of what I have:
public async Task LoadList()
{
...
// get data
Uri uri = new Uri("https://...");
response = await httpClient.GetAsync(uri);
// display
BeginInvokeOnMainThread () =>
{
... update the UI ...
});
}
But I get the error CS0103 The name 'BeginInvokeOnMainThread' does not exist in the current context UnoTest.Droid, UnoTest.UWP, UnoTest.Wasm
BeginInvokeOnMainThread / Dispatcher.Invoke / Control.Invoke were never a good idea.
Uno should have a SynchronizationContext that is automatically used by await, so manual thread marshaling should not be necessary:
public async Task LoadList()
{
...
// get data
Uri uri = new Uri("https://...");
response = await httpClient.GetAsync(uri);
// display
... update the UI ...
}
I am currently using the Event Store to handle my events. I currently need to replay a particular type of event as I have made changes in the way they are subscribed and written to DB.
Is this possible? If so, how can it be done? Thanks.
You cannot tell EventStore to replay a specific event onto a persistent subscription because the point of the persistent subscription is to keep state for the subscribers.
To achieve this kind of fix you would really need a catch up application to do the work.
And really if you think about, if you replayed ALL the events to a new database then you would have the correct data in there?
So I have a console application that reuses the same logic as the persistent connection but the only difference is:
I change the target database connection string - So this would be a new Database or Collection (not the broken one)
It connects to EventStore and replays all the events from the start
It rebuilds the entire database to the correct state
Switch the business over to the new database
This is the point of EventStore - You just replay all the events to build any database at any time and it will be correct
Your persistent connections deal with new, incoming events and apply updates.
If you enable $by_event_type projection than you can access that projection stream under
/streams/$et-{event-type}
https://eventstore.org/docs/projections/system-projections/index.html
Then you can read it using .net api if you wish.
Here is some code to get you started
private static T GetInstanceOfEvent<T>(ResolvedEvent resolvedEvent) where T : BaseEvent
{
var metadataString = Encoding.UTF8.GetString(resolvedEvent.Event.Metadata);
var eventClrTypeName = JObject.Parse(metadataString).Property(EventClrTypeHeader).Value;
var #event = JsonConvert.DeserializeObject(Encoding.UTF8.GetString(resolvedEvent.Event.Data), Type.GetType((string) eventClrTypeName));
if (!(#event is BaseEvent))
{
throw new MessageDeserializationException((string) eventClrTypeName, metadataString);
}
return #event as T;
}
private static IEventStoreConnection GetEventStoreConnection()
{
var connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["EventStore"].ConnectionString;
var connection = EventStoreConnection.Create(connectionString);
connection.ConnectAsync().Wait();
return connection;
}
private static string GetStreamName<T>() where T : BaseEvent
{
return "$et-" + typeof(T).Name;
}
And to read events you can use this code snippet
StreamEventsSlice currentSlice;
long nextSliceStart = StreamPosition.Start;
const int sliceCount = 200;
do
{
currentSlice = await esConnection.ReadStreamEventsForwardAsync(streamName, nextSliceStart, sliceCount, true);
foreach (var #event in currentSlice.Events)
{
var myEvent = GetInstanceOfEvent<OrderMerchantFeesCalculatedEvent>(#event);
TransformEvent(myEvent);
}
nextSliceStart = currentSlice.NextEventNumber;
} while (currentSlice.IsEndOfStream == false);
I'm a new in the async world. Regarding your static method (from https://stackoverflow.com/a/25733275/1596974):
static async Task<TResult[]> WhenAll<TResult>(IEnumerable<Task<TResult>> tasks, TimeSpan timeout)
{
var timeoutTask = Task.Delay(timeout).ContinueWith(_ => default(TResult));
var completedTasks =
(await Task.WhenAll(tasks.Select(task => Task.WhenAny(task, timeoutTask)))).
Where(task => task != timeoutTask);
return await Task.WhenAll(completedTasks);
}
How should I use it in order to retrieve the results of those tasks?
Just to be clear, what I need to achieve here is basically this:
For each task I'm calling to several shipping providers in order to get the different shipping rates from them.
Aggregate the response from all the shipping providers into a big list of shipping rates.
Sometimes one (or more) of the shipping providers can be down. So, I need to retrieve the shipping rates from the tasks that completed successfully and just skip the ones that failed.
I hope I was clear enough.
Ok, I ended up with this code that worked pretty well:
var providers = GetShippingProviders().ToList();
var tasks = new Task<Task>[providers.Count];
var timeout = TimeSpan.FromMilliseconds(10000);
try
{
var shippingRates = new List<IShippingRate>();
for (var i = 0; i < tasks.Length; i++)
{
var provider = providers[i];
tasks[i] = Task.WhenAny(Task.Run(() => provider.GetShippingRates(origin, destination, weight)), Task.Delay(timeout));
}
Task.WaitAll(tasks);
foreach (var tasksResult in tasks.Select(x => x.Result).Where(x => x.Status == TaskStatus.RanToCompletion))
{
var shippingRatesResult = tasksResult as Task<List<IShippingRate>>;
if (shippingRatesResult != null)
shippingRates.AddRange(shippingRatesResult.Result.ToList());
}
}
catch (AggregateException ae)
{
Log.Error("An exception occurred when retrieving the shipping Rates.", ae.Flatten());
}
All the tasks that completed successfully are processed. The ones that failed can be just skipped. There is a way to add some code using the "Task.ContinueWith(...)" so the faulted tasks can be catched for logging the exceptions as well.
For the ones that fail, do they throw an exception? Or do they just hang for a long time?
I might do something like this:
var shippingProviderRateTasks = ...;
var results = ...;
foreach (var task in shippingProviderRateTasks) {
try {
results.Add(await task);
} catch (Exception e) {
// log the error here, if you want, and skip this provider
}
}
One of the primary reasons to use Task.WhenAll is to catch an exception when it occurs, and not later on. If you want to swallow all the exceptions and essentially ignore those errors, you might as well just await each of them one at a time - it shouldn't be any slower.
I have a Action that sends a simple email:
[HttpPost, ActionName("Index")]
public ActionResult IndexPost(ContactForm contactForm)
{
if (ModelState.IsValid)
{
new EmailService().SendAsync(contactForm.Email, contactForm.Name, contactForm.Subject, contactForm.Body, true);
return RedirectToAction(MVC.Contact.Success());
}
return View(contactForm);
}
And a email service:
public void SendAsync(string fromEmail, string fromName, string subject, string body, bool isBodyHtml)
{
MailMessage mailMessage....
....
SmtpClient client = new SmtpClient(settingRepository.SmtpAddress, settingRepository.SmtpPort);
client.EnableSsl = settingRepository.SmtpSsl;
client.Credentials = new NetworkCredential(settingRepository.SmtpUserName, settingRepository.SmtpPassword);
client.SendCompleted += client_SendCompleted;
client.SendAsync(mailMessage, Tuple.Create(client, mailMessage));
}
private void client_SendCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
{
Tuple<SmtpClient, MailMessage> data = (Tuple<SmtpClient, MailMessage>)e.UserState;
data.Item1.Dispose();
data.Item2.Dispose();
if (e.Error != null)
{
}
}
When I send a email, I am using Async method, then my method SendAsync return immediately, then RedirectToAction is called. But the response(in this case a redirect) isn´t sent by ASP.NET until client_SendCompleted is completed.
Here's what I'm trying to understand:
When watching the execution in Visual Studio debugger, the SendAsync returns immediately (and RedirectToAction is called), but nothing happens in the browser until email is sent?
If i put a breakpoint inside client_SendCompleted, the client stay at loading.... until I hit F5 at debugger.
This is by design. ASP.NET will automatically wait for any outstanding async work to finish before finishing the request if the async work was kicked off in a way that calls into the underlying SynchronizationContext. This is to ensure that if your async operation tries to interact with the HttpContext, HttpResponse, etc. it will still be around.
If you want to do true fire & forget, you need to wrap your call in ThreadPool.QueueUserWorkItem. This will force it to run on a new thread pool thread without going through the SynchronizationContext, so the request will then happily return.
Note however, that if for any reason the app domain were to go down while your send was still in progress (e.g. if you changed the web.config file, dropped a new file into bin, the app pool recycled, etc.) your async send would be abruptly interrupted. If you care about that, take a look at Phil Haacks WebBackgrounder for ASP.NET, which let's you queue and run background work (like sending an email) in such a way that will ensure it gracefully finishes in the case the app domain shuts down.
This is an interesting one. I've reproduced the unexpected behaviour, but I can't explain it. I'll keep digging.
Anyway the solution seems to be to queue a background thread, which kind of defeats the purpose in using SendAsync. You end up with this:
MailMessage mailMessage = new MailMessage(...);
SmtpClient client = new SmtpClient(...);
client.SendCompleted += (s, e) =>
{
client.Dispose();
mailMessage.Dispose();
};
ThreadPool.QueueUserWorkItem(o =>
client.SendAsync(mailMessage, Tuple.Create(client, mailMessage)));
Which may as well become:
ThreadPool.QueueUserWorkItem(o => {
using (SmtpClient client = new SmtpClient(...))
{
using (MailMessage mailMessage = new MailMessage(...))
{
client.Send(mailMessage, Tuple.Create(client, mailMessage));
}
}
});
With .Net 4.5.2, you can do this with ActionMailer.Net:
var mailer = new MailController();
var msg = mailer.SomeMailAction(recipient);
var tcs = new TaskCompletionSource<MailMessage>();
mailer.OnMailSentCallback = tcs.SetResult;
HostingEnvironment.QueueBackgroundWorkItem(async ct =>
{
msg.DeliverAsync();
await tcs.Task;
Trace.TraceInformation("Mail sent to " + recipient);
});
Please read this first: http://www.hanselman.com/blog/HowToRunBackgroundTasksInASPNET.aspx
I sent the bug to Microsoft Connect https://connect.microsoft.com/VisualStudio/feedback/details/688210/smtpclient-sendasync-blocking-my-asp-net-mvc-request