Database.CQRS.Stream

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

Documentation

class Stream f stream where

Associated Types

type EventType stream :: *

Type of the events contained in that stream.

type EventIdentifier stream :: *

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 :: *

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 ()

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)

Defined in Database.CQRS.InMemory

Associated Types

type EventType (Stream metadata event) :: Type

type EventIdentifier (Stream metadata event) :: Type

type EventMetadata (Stream metadata event) :: Type

Methods

streamEvents :: Stream metadata event -> StreamBounds' (Stream metadata event) -> Producer [Either (EventIdentifier (Stream metadata event), String) (EventWithContext' (Stream metadata event))] m ()

Monad m => Stream m (TransformedStream m identifier metadata event)

Defined in Database.CQRS.Transformer

Associated Types

type EventType (TransformedStream m identifier metadata event) :: Type

type EventIdentifier (TransformedStream m identifier metadata event) :: Type

type EventMetadata (TransformedStream m identifier metadata event) :: Type

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 ()

class Stream f stream => WritableStream f stream where

Methods

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

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)

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))

data EventWithContext identifier metadata event

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)

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)

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)

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)

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)

class MonadMetadata metadata m where

The event metadata come from the current "environment".

Methods

getMetadata :: m metadata

Instances

Monad m => MonadMetadata () m

Defined in Database.CQRS.Stream

Methods

getMetadata :: m ()

data ConsistencyCheck identifier

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)

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)

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

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

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

Defined in Database.CQRS.Stream

Methods

fmap :: (a -> b) -> StreamBounds a -> StreamBounds b

(<$) :: a -> StreamBounds b -> StreamBounds a

Foldable StreamBounds

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

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)

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)

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)

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

After the event with the given identifier, excluding it.

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

Until the event with the given identifier, including it.