Safe Haskell	None
Language	Haskell2010

Eventium.CommandHandler

Description

Defines a Command Handler type.

Synopsis

data CommandHandler state event command = CommandHandler {
- commandHandlerHandler :: state -> command -> [event]
- commandHandlerProjection :: Projection state event
}
allCommandHandlerStates :: CommandHandler state event command -> [command] -> [state]
applyCommandHandler :: Monad m => VersionedEventStoreWriter m event -> VersionedEventStoreReader m event -> CommandHandler state event command -> UUID -> command -> m [event]
serializedCommandHandler :: CommandHandler state event command -> Serializer event serializedEvent -> Serializer command serializedCommand -> CommandHandler state serializedEvent serializedCommand

Documentation

data CommandHandler state event command Source #

An CommandHandler is a combination of a Projection and a function to validate commands against that Projection. When using a command handler 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

CommandHandler
Fields commandHandlerHandler :: state -> command -> [event] commandHandlerProjection :: Projection state event

allCommandHandlerStates :: CommandHandler state event command -> [command] -> [state] Source #

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

applyCommandHandler :: Monad m => VersionedEventStoreWriter m event -> VersionedEventStoreReader m event -> CommandHandler state event command -> UUID -> command -> m [event] Source #

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

serializedCommandHandler :: CommandHandler state event command -> Serializer event serializedEvent -> Serializer command serializedCommand -> CommandHandler state serializedEvent serializedCommand Source #

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