7.0.0: Async Events & Cancellation Tokens

Overview

Custom event handlers have been changed to use the asynchonrous variant. This is seen as a positive step forward as more libraries adopt the asynchonrous programming paradigm. By utilizng asynchonrous handlers, observers can avoid utilizing async void implementations whereever a need for asynchonrous exists. Clarity has also been provided on cancellations, which in the past, where supported for every event, even if this was not the original intention. Cancellation tokens have also been added as optional parameters to every public and protected method, facilitating top level cancellation by allowing the token to be propagated throughout the solution.

Enhancements

• Added a new ToGuid method to Ddd.SignedVersion, enabling the caller to produce a GUID based on the Header and Footer of the version.
• Added a new Ddd.Collections.UnversionedReferenceDictionary to simplify lookups based on reference when aggregate versioning does not apply.
• Added a new Ddd.Collections.DictionaryExtensions.ToUnversioned to simplify conversion of an existing dictionary into an unversioned variant.
• Added a new Ddd.Collections.EnumerableExtensions.ToUnversionedDictionary to simplify conversion of an existing collection of aggregates or projections into an unversioned index of the same.
• Added a new Ddd.ReferenceExtensions.ToUnversioned extension to facilitate the creation of an unversioned reference based on the reference supplied if that reference was versioned, otherwise it will return the same reference.
• Added a new Ddd.Services.IAggregateFactory to support aggregate creation when the explicit type is not known.
• Added a new Ddd.Services.CoordinatedHandler to support coordinated handling of generic operations in the context of an aggregate type.
• Added a new Ddd.Services.DefaultAggregateFactory to provide a default implementation for aggregate creation when the explicit type is not known.
• Added a TimeStamp to Ddd.SignedVersion which defaults to MinValue if no value was previously serialized.
• Applied optional cancellation tokens to every public and protected async method, thereby facilitating propagation of cancellation tokens (Breaking Change).
• Changed Ddd.AggregateRootExtensions.ToReference to include an optional switch to facilitate creation of an unversioned reference for the aggregate supplied.
• Changed Ddd.Services.AggregateSavedEventHandler to an async variant named AggregateSavedAsyncEventHandler (Breaking Change).
• Changed Ddd.Services.AggregateSavingAsyncEventHandler to an async variant named AggregateSavingAsyncEventHandler (Breaking Change).
• Changes Ddd.Services.CoordinatedGenerateHandler to inherit from Ddd.Services.CoordinatedHandler.
• Changed Ddd.Services.DomainEventsPublishedEventHandler to an async variant named DomainEventsPublishedAsyncEventHandler (Breaking Change).
• Changed Ddd.Services.DomainEventsPublishingEventHandler to an async variant named DomainEventsPublishingAsyncEventHandler (Breaking Change).
• Changed Ddd.Services.Reconciliation.AggregateConflictDetectedEventHandler to an async variant named AggregateConflictDetectedAsyncEventHandler (Breaking Change).
• Changed Ddd.Services.Reconciliation.AggregateReconciledEventHandler to an async variant named AggregateReconciledAsyncEventHandler (Breaking Change).
• Changed Ddd.Services.Reconciliation.IAggregateReconciliationProxy so that it no longer implements CreateAsync (Breaking Change).
• Changed Ddd.Services.Reconciliation.EventsReconciledEventHandler to an async variant named EventsReconciledAsyncEventHandler (Breaking Change).
• Changed Ddd.Services.Reconciliation.EventsReconcilingEventHandler to an async variant named EventsReconcilingAsyncEventHandler (Breaking Change).
• Changed Ddd.Services.Reconciliation.EventSequenceAdvancedEventHandler to an async variant named EventSequenceAdvancedAsyncEventHandler (Breaking Change).
• Changed Ddd.Services.Reconciliation.SnapshotRestorationCompletedEventHandler to an async variant named SnapshotRestorationCompletedAsyncEventHandler (Breaking Change).
• Changed Ddd.Services.Reconciliation.SnapshotRestorationCommencingEventHandler to an async variant named SnapshotRestorationCommencingAsyncEventHandler (Breaking Change).
• Changed Ddd.Services.Repository so that it now implements IEmitDiagnostics.
• Changed Services.Bus so that it now implements IEmitDiagnostics.
• Changed Services.MessageInvokedEventHandler to an async variant named MessageInvokedAsyncEventHandler (Breaking Change).
• Changed Services.MessageInvokingEventHandler to an async variant named MessageInvokingAsyncEventHandler (Breaking Change).
• Changed the invocation of the AggregateReconciled event handler of Ddd.Services.AggregateReconciler to utilize the passive implementation (Breaking Change).
• Changed the invocation of the AggregateSaved event handler of Ddd.Services.Repository to utilize the passive implementation (Breaking Change).
• Changed the invocation of the EventsReconciled event handler of Ddd.Services.Reconciliation.EventReconciler to utilize the passive implementation (Breaking Change).
• Changed the invocation of the Published event handler of Ddd.Services.Bus to utilize the passive implementation (Breaking Change).
• Changed the invocation of the Invoked event handler of Services.Bus to utilize the passive implementation (Breaking Change).
• Changed the invocation of the SequenceAdvanced event handler of Ddd.Services.Reconciliation.EventReconciler to utilize the passive implementation (Breaking Change).
• Removed Ddd.Services.Reconciliation.SynchronousAggregateReconciler due to inherrant challenges presented by the event driven feedback model (Breaking Change).
• Renamed Ddd.ReferenceExtensions.ToTypedReference to Ddd.ReferenceExtensions.ToTyped (Breaking Change).

End-User Impact

In many cases, it is expected that event handlers can be updated by simply:

1. Changing the return type from void to Task.
2. Returning Task.CompletedTask.

Passive handlers will no longer require that the observer handle exceptions.