Eventful.Aggregate

Defines an Aggregate type-class from DDD parlance.

Documentation

data Aggregate state event command

An Aggregate is a combination of a Projection and a function to validate commands against that Projection. When using an aggregate in some service, it is common to simply load the latest projection state from the event store and handle the command. If the command is valid then the new events are applied to the projection in the event store.

Constructors

Aggregate

Fields

• aggregateCommandHandler :: state -> command -> [event]
• aggregateProjection :: Projection state event

allAggregateStates :: Aggregate state event command -> [command] -> [state]

Given a list commands, produce all of the states the aggregate's projection sees. This is useful for unit testing aggregates.

commandStoredAggregate :: Monad m => EventStore serialized m -> Aggregate state serialized command -> UUID -> command -> m [serialized]

Loads the latest version of a Projection from the event store and tries to apply the Aggregate command to it. If the command succeeds, then this saves the events back to the store as well.

serializedAggregate :: Aggregate state event command -> Serializer event serializedEvent -> Serializer command serializedCommand -> Aggregate state serializedEvent serializedCommand

Use a pair of Serializers to wrap a Aggregate with event type event and command type command so it uses the serializedEvent and serializedCommand types.