Safe Haskell	Safe
Language	Haskell2010

Database.CQRS.Stream

Description

Events can be written to a stream and can be streamed from it.

Synopsis

class Stream f stream where
- type EventType stream :: *
- type EventIdentifier stream :: *
- type EventMetadata stream :: *
- streamEvents :: stream -> StreamBounds' stream -> Producer [Either (EventIdentifier stream, String) (EventWithContext' stream)] f ()
class Stream f stream => WritableStream f stream where
- writeEventWithMetadata :: stream -> EventType stream -> EventMetadata stream -> ConsistencyCheck (EventIdentifier stream) -> f (EventIdentifier stream)
data EventWithContext identifier metadata event = EventWithContext {
- identifier :: identifier
- metadata :: metadata
- event :: event
}
type EventWithContext' stream = EventWithContext (EventIdentifier stream) (EventMetadata stream) (EventType stream)
class MonadMetadata metadata m where
- getMetadata :: m metadata
data ConsistencyCheck identifier
- = NoConsistencyCheck
- | CheckNoEvents
- | CheckLastEvent identifier
writeEvent :: (Monad m, MonadMetadata (EventMetadata stream) m, WritableStream m stream) => stream -> EventType stream -> m (EventIdentifier stream)
writeEventCc :: (Monad m, MonadMetadata (EventMetadata stream) m, WritableStream m stream) => stream -> EventType stream -> ConsistencyCheck (EventIdentifier stream) -> m (EventIdentifier stream)
optimistically :: MonadError Error m => m a -> m a
data StreamBounds identifier = StreamBounds {
- _afterEvent :: Maybe identifier
- _untilEvent :: Maybe identifier
}
type StreamBounds' stream = StreamBounds (EventIdentifier stream)
afterEvent :: Ord identifier => identifier -> StreamBounds identifier
untilEvent :: Ord identifier => identifier -> StreamBounds identifier

Documentation

class Stream f stream where Source #

Associated Types

type EventType stream :: * Source #

Type of the events contained in that stream.

type EventIdentifier stream :: * Source #

Type of unique identifiers for events in the stream.

There must be a total order on identifiers so they can be sorted.

type EventMetadata stream :: * Source #

Depending on the store, this structure can contain the creation date, a correlation ID, etc.

Methods

streamEvents :: stream -> StreamBounds' stream -> Producer [Either (EventIdentifier stream, String) (EventWithContext' stream)] f () Source #

Stream all the events within some bounds in arbitrary batches.

Events must be streamed from lowest to greatest identifier. If the back-end is fetching events in batches, they can be returned in the same way to improve performace. If the event can't be decoded, a Left should be returned instead with the identifier and an error message.

Instances

MonadIO m => Stream m (Stream metadata event) Source #
Instance details Defined in Database.CQRS.InMemory Associated Types type EventType (Stream metadata event) :: Type Source # type EventIdentifier (Stream metadata event) :: Type Source # type EventMetadata (Stream metadata event) :: Type Source # Methods streamEvents :: Stream metadata event -> StreamBounds' (Stream metadata event) -> Producer [Either (EventIdentifier (Stream metadata event), String) (EventWithContext' (Stream metadata event))] m () Source #
Monad m => Stream m (TransformedStream m identifier metadata event) Source #
Instance details Defined in Database.CQRS.Transformer Associated Types type EventType (TransformedStream m identifier metadata event) :: Type Source # type EventIdentifier (TransformedStream m identifier metadata event) :: Type Source # type EventMetadata (TransformedStream m identifier metadata event) :: Type Source # Methods streamEvents :: TransformedStream m identifier metadata event -> StreamBounds' (TransformedStream m identifier metadata event) -> Producer [Either (EventIdentifier (TransformedStream m identifier metadata event), String) (EventWithContext' (TransformedStream m identifier metadata event))] m () Source #

class Stream f stream => WritableStream f stream where Source #

Methods

writeEventWithMetadata :: stream -> EventType stream -> EventMetadata stream -> ConsistencyCheck (EventIdentifier stream) -> f (EventIdentifier stream) Source #

Append the event to the stream and return the identifier.

The identifier must be greater than the previous events' identifiers.

The function must throw ConsistencyCheckError if the check fails.

Instances

(MonadError Error m, MonadIO m, NFData event, NFData metadata) => WritableStream m (Stream metadata event) Source #
Instance details Defined in Database.CQRS.InMemory Methods writeEventWithMetadata :: Stream metadata event -> EventType (Stream metadata event) -> EventMetadata (Stream metadata event) -> ConsistencyCheck (EventIdentifier (Stream metadata event)) -> m (EventIdentifier (Stream metadata event)) Source #

data EventWithContext identifier metadata event Source #

Once added to the stream, an event is adorned with an identifier and some metadata.

Constructors

EventWithContext
Fields identifier :: identifier metadata :: metadata event :: event

Instances

(Eq identifier, Eq metadata, Eq event) => Eq (EventWithContext identifier metadata event) Source #
Instance details Defined in Database.CQRS.Stream Methods (==) :: EventWithContext identifier metadata event -> EventWithContext identifier metadata event -> Bool # (/=) :: EventWithContext identifier metadata event -> EventWithContext identifier metadata event -> Bool #
(Show identifier, Show metadata, Show event) => Show (EventWithContext identifier metadata event) Source #
Instance details Defined in Database.CQRS.Stream Methods showsPrec :: Int -> EventWithContext identifier metadata event -> ShowS # show :: EventWithContext identifier metadata event -> String # showList :: [EventWithContext identifier metadata event] -> ShowS #
Generic (EventWithContext identifier metadata event) Source #
Instance details Defined in Database.CQRS.Stream Associated Types type Rep (EventWithContext identifier metadata event) :: Type -> Type # Methods from :: EventWithContext identifier metadata event -> Rep (EventWithContext identifier metadata event) x # to :: Rep (EventWithContext identifier metadata event) x -> EventWithContext identifier metadata event #
type Rep (EventWithContext identifier metadata event) Source #
Instance details Defined in Database.CQRS.Stream type Rep (EventWithContext identifier metadata event) = D1 (MetaData "EventWithContext" "Database.CQRS.Stream" "eventsourcing-0.9.0-4g8y83fLOKaCrH4ufVC9GA" False) (C1 (MetaCons "EventWithContext" PrefixI True) (S1 (MetaSel (Just "identifier") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 identifier) :: (S1 (MetaSel (Just "metadata") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 metadata) :: S1 (MetaSel (Just "event") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 event))))

type EventWithContext' stream = EventWithContext (EventIdentifier stream) (EventMetadata stream) (EventType stream) Source #

class MonadMetadata metadata m where Source #

The event metadata come from the current "environment".

Methods

getMetadata :: m metadata Source #

Instances

Monad m => MonadMetadata () m Source #
Instance details Defined in Database.CQRS.Stream Methods getMetadata :: m () Source #

data ConsistencyCheck identifier Source #

A condition to check before inserting a new event in a stream.

This can be used to enforce consistency by checking that no new events were inserted since some validation has been performed and therefore that the validations are still sound.

Constructors

NoConsistencyCheck	Always write the new event.
CheckNoEvents	There are no events in that stream.
CheckLastEvent identifier	The latest event's identifier matches.

writeEvent :: (Monad m, MonadMetadata (EventMetadata stream) m, WritableStream m stream) => stream -> EventType stream -> m (EventIdentifier stream) Source #

Get the metadata from the environment, append the event to the store and return the identifier.

writeEventCc :: (Monad m, MonadMetadata (EventMetadata stream) m, WritableStream m stream) => stream -> EventType stream -> ConsistencyCheck (EventIdentifier stream) -> m (EventIdentifier stream) Source #

Get the metadata from the environment, validate the consistency check, append the event to the store and return its identifier.

optimistically :: MonadError Error m => m a -> m a Source #

Execute an action and retry indefinitely as long as it throws ConsistencyCheckError.

This makes it possible to have Optimistic Concurrency Control when writing events by getting the aggregate and using writeEventCc or writeEventWithMetadata inside the action passed to optimistically.

/! It does NOT create a transaction when you can write several events. You should only use this to write a single event!

data StreamBounds identifier Source #

Lower/upper bounds of an event stream.

The Semigroup instance returns bounds for the intersection of the two streams.

Constructors

StreamBounds
Fields _afterEvent :: Maybe identifier Exclusive. _untilEvent :: Maybe identifier Inclusive.

Instances

Functor StreamBounds Source #
Instance details Defined in Database.CQRS.Stream Methods fmap :: (a -> b) -> StreamBounds a -> StreamBounds b # (<$) :: a -> StreamBounds b -> StreamBounds a #
Foldable StreamBounds Source #
Instance details Defined in Database.CQRS.Stream Methods fold :: Monoid m => StreamBounds m -> m # foldMap :: Monoid m => (a -> m) -> StreamBounds a -> m # foldr :: (a -> b -> b) -> b -> StreamBounds a -> b # foldr' :: (a -> b -> b) -> b -> StreamBounds a -> b # foldl :: (b -> a -> b) -> b -> StreamBounds a -> b # foldl' :: (b -> a -> b) -> b -> StreamBounds a -> b # foldr1 :: (a -> a -> a) -> StreamBounds a -> a # foldl1 :: (a -> a -> a) -> StreamBounds a -> a # toList :: StreamBounds a -> [a] # null :: StreamBounds a -> Bool # length :: StreamBounds a -> Int # elem :: Eq a => a -> StreamBounds a -> Bool # maximum :: Ord a => StreamBounds a -> a # minimum :: Ord a => StreamBounds a -> a # sum :: Num a => StreamBounds a -> a # product :: Num a => StreamBounds a -> a #
Traversable StreamBounds Source #
Instance details Defined in Database.CQRS.Stream Methods traverse :: Applicative f => (a -> f b) -> StreamBounds a -> f (StreamBounds b) # sequenceA :: Applicative f => StreamBounds (f a) -> f (StreamBounds a) # mapM :: Monad m => (a -> m b) -> StreamBounds a -> m (StreamBounds b) # sequence :: Monad m => StreamBounds (m a) -> m (StreamBounds a) #
Ord identifier => Semigroup (StreamBounds identifier) Source #
Instance details Defined in Database.CQRS.Stream Methods (<>) :: StreamBounds identifier -> StreamBounds identifier -> StreamBounds identifier # sconcat :: NonEmpty (StreamBounds identifier) -> StreamBounds identifier # stimes :: Integral b => b -> StreamBounds identifier -> StreamBounds identifier #
Ord identifier => Monoid (StreamBounds identifier) Source #
Instance details Defined in Database.CQRS.Stream Methods mempty :: StreamBounds identifier # mappend :: StreamBounds identifier -> StreamBounds identifier -> StreamBounds identifier # mconcat :: [StreamBounds identifier] -> StreamBounds identifier #

type StreamBounds' stream = StreamBounds (EventIdentifier stream) Source #

afterEvent :: Ord identifier => identifier -> StreamBounds identifier Source #

After the event with the given identifier, excluding it.

untilEvent :: Ord identifier => identifier -> StreamBounds identifier Source #

Until the event with the given identifier, including it.