private void handleMessage
(BrokeredMessage message)
{
if (message == null)
{
throw new ArgumentNullException(nameof(message));
}
// When the service is stopped we call the close method on the
// topic. The following guard statement is needed because there
// can be a delay between calling close on the topic and it
// stopping the message pump.
if (ingressTopicSubscription != null &&
!ingressTopicSubscription.IsClosed)
{
Trace.TraceInformation($"[{message.MessageId}] Received message");
var dataModel
= new DataModelDbContext();
try {
Trace.TraceInformation($"[{message.MessageId}] Processing message");
processMessageInServiceLayer(
dataModel,
message,
serviceCommandFactory
);
message.Complete();
// Note - The audit domain is a essentially a query domain it
// records informations to allow querying for audit events
// as such it does not trigger any events which is why
// after completing the message there is not more processing
// need to ensure that the message has been handled correctly/
Trace.TraceInformation($"[{message.MessageId}] Completed message");
} catch (Exception e) {
Trace.TraceError($"[{message.MessageId}] Error - Message: {e.Message}, Stack trace: {e.StackTrace}");
throw;
} finally {
dataModel.Dispose();
}
}
}
private static void processMessageInServiceLayer
(DataModelDbContext dataModel
, BrokeredMessage message
, ServiceCommandFactory serviceCommandFactory)
{
if (dataModel == null)
{
throw new ArgumentNullException(nameof(dataModel));
}
if (message == null)
{
throw new ArgumentNullException(nameof(message));
}
if (serviceCommandFactory == null)
{
throw new ArgumentNullException(nameof(serviceCommandFactory));
}
var messageId
= Guid.Parse(message.MessageId);
// If there is an exception between before the commit you do not
// want to complete the message. If there there is a problem
// between the commit and the message being completed then we
// have a message that will be processed twice so we take the
// hit and just check to see if we have seen the message before
// and if so just return and let the message be cleared of the
// subscription.
if (dataModel.HasSeenMessage(messageId))
{
return;
}
var transaction
= dataModel
.Database
.BeginTransaction(IsolationLevel.Serializable);
try {
dataModel
.AddMessageAsSeen(messageId);
var serviceRequest
= new ServiceRequest(
dataModel
, Guid.Parse(message.CorrelationId)
, messageId
, TopicSourceName
, message.ContentType
, message.GetBody <string>()
, DateTime.Now
);
// Because topics are heterogeneous we need to identify the
// correct service command for the message. Different messages
// have different handlers.
//
// It may be valid that we are not interested in auditing
// certain messages in which case we need a default handler.
serviceCommandFactory[message.ContentType]
.Match(
just: serviceCommand => serviceCommand
, nothing: () => new UnhandledMessage()
)
.Handle(serviceRequest);
dataModel.SaveChanges();
transaction.Commit();
} finally {
transaction.Dispose();
}
}