EventStoreAdapter.md

Introduction

The event store is a place where all events are persisted.

Every adapter needs to expose a function that takes an options object as argument and returns an object (or a class instance) with the following functions.

Reference

Visibility	Property
public	async init() Initializes the adapter
public	async save(event: object): int | false Saves an event
public	async load(filter: object): object Loads events
public	async delete(aggregateId: string): number Removes every event of the specified aggregate id
public	async close() Closes the event store

init

async init()
Initializes the adapter.

save

async save(event: object): int | false
Saves the event passed to it.

Parameters

Name	Type	Attribute	Description
event	object		The event to be saved

Return

The position (number) of the event inside the event store or false if the new position of the event is already taken (conflict).

Examples

const position = await eventStore.save({
    id: 'b42e61d5-e911-4ea8-92fd-57ceb552e712',
    aggregateId: '4233fb22-76eb-4b8f-9b34-8fdcb994e370',
    aggregateVersion: 0,
    type: 'ANSWER_CREATED',
    timestamp: Date.now(),
    correlationId: '4233fb22-76eb-4b8f-9b34-8fdcb994e370',
    causationId: null,
    payload: {
        answer: 42
    }
});

load

async load(filter: object): object
Loads all events from the event store that match the passed filter.

Parameters

Name	Type	Attribute	Description
filter	object		An object containing conditions

Filter

Property	Type	Attribute	Description
aggregateIds	array	optional	An array of strings with the desired aggregate IDs
types	array	optional	An array of strings with the desired event types
correlationIds	array	optional	An array of strings with the desired correlation IDs
causationIds	array	optional	An array of strings with the desired causation IDs
since	int	optional	To exclude events with a timestamp < since
until	int	optional	To exclude events with a timestamp >= until
limit	int	optional	To limit the number of returned events
reverse	boolean	optional default: false	To reverse the order of the events
cursor	mixed | null	optional	A cursor to scroll the result if a limit was used

Return

An object containing the keys events and cursor.

Property	Type	Attribute	Description
events	array		An array that contains the matching events
cursor	mixed		A cursor that can be passed to another call to load to scroll the result

An event that was loaded contains the additional property position that was given to the event during save.
So an event may look like this:

{
    "id": "b42e61d5-e911-4ea8-92fd-57ceb552e712",
    "position": 423,
    "aggregateId": "4233fb22-76eb-4b8f-9b34-8fdcb994e370",
    "aggregateVersion": 0,
    "type": "ANSWER_CREATED",
    "timestamp": 123456789,
    "correlationId": "4233fb22-76eb-4b8f-9b34-8fdcb994e370",
    "causationId": null,
    "payload": {
        "answer": 42
    }
}

Examples

const {events, cursor} = await eventStore.load({
    aggregateIds: [
        '4233fb22-76eb-4b8f-9b34-8fdcb994e370'
    ],
    types: [
        'ANSWER_CREATED',
        'ANSWER_UPDATED'
    ],
    since: Date.now() - 1000*60*60*24,
    until: Date.now(),
    limit: 5,
    cursor: null
});

delete

async delete(aggregateId: string): number
Deletes all events that belong to the specified aggregate id.

Parameters

Name	Type	Attribute	Description
aggregateId	string		The aggregate id

Return

The amount (number) of events that were deleted.

Examples

const eventCount = await eventStore.delete('4233fb22-76eb-4b8f-9b34-8fdcb994e370');

close

async close()
Securely closes all open connections to the database server.