demeine

demeine
=======

Demeine is a library supporting DDDD (Distributed Domain Drive Design).

* Purpose
* Installation
* Usage
* Components
* Aggregate
* clearUncommittedEvents
* delete
* getUncommittedEvents
* getUncommittedEventsAsync
* getVersion
* Repository
* checkConcurrencyStrategy
* findById
* findByQueryStreamWithSnapshot
* findBySnapshot
* findEventsById
* save

Purpose

Provide the base building blocks for implementing DDD in a distributed environment. This repository contains an
implementation of a _repository_, as well as a base _aggregate_ that domain specific aggregates can extend. The flow of
action → command → event → state update is supported.

Installation

``shell
npm install demeine
`

Usage

This example uses TapeWORM with its default in memory partition.

`ts
// User.ts
export const USER_AGGREGATE_TYPE = 'user';

export interface UserState {
id: string;
name: string;
}

export class User extends Aggregate {
constructor(commandSink?: CommandSink, eventHandler?: EventHandler, commandHandler?: CommandHandler) {
super(commandSink, eventHandler, commandHandler);

this._state = {
id: this.id,
name: ''
};
}

register(id: string, name: string) {
this.id = id;

return this._sink({
type: 'user.register.command',
payload: { id, name },
aggregateId: this.id
});
}

processChangeName(command: Command) {
return this._apply(
{
type: 'location.name_changed.event',
payload: command.payload,
aggregateId:
this.id
},
true
);
}

applyNameChanged(event: Event) {
this._state.name = event.payload.name;
}
}

// userFactory.ts
import { User, UserState, USER_AGGREGATE_TYPE } from './User';

export function userFactory(id: string) {
const user = new User();

user.id = id;
user._state = { id, name: '' };
user.type = USER_AGGREGATE_TYPE;

return user;
}

// index.ts
import { Aggregate, Repository } from 'demeine';
import TapeWorm from 'tapeworm';
import { User, USER_AGGREGATE_TYPE } from './User';
import { userFactory } from './userFactory';

const tapeWorm = new TapeWorm();
const partition = await tapeWorm.openPartition('my_partition');

const userRepository = new Repository(partition, USER_AGGREGATE_TYPE, userFactory);

// Not found, name: ''
const user = await userRepository.findById('123');
await user.register('123', 'Jeff');
await userRepository.save(user);

// Exists since save(user), name: 'Jeff'
const existingUser = await userRepository.findById('123');
`

Components

$3

Base class for aggregate classes representing domain concepts.

#### clearUncommittedEvents

Remove the events created through calling the aggregate methods.

Is used in the save method on the Repository in order to remove local events after they've been committed.

`typescript
const user = await userRepository.findById('123');

// Adds user.registered.event to uncommitted events
await user.register('123', 'Jeff');
// Removes the registered event
await user.clearUncommittedEvents();

await userRepository.save(user);
`

#### delete

Creates a $stream.deleted.event for the aggregate, which the persistence partition should handle by removing the
aggregate data.

`typescript
const user = await userRepository.findById('123');
await user.delete();
await userRepository.save(user);

// Should not exist anymore
const nonExistingUser = await userRepository.findById('123');
`

#### getUncommittedEvents

Retrieves the list of events created by calling aggregate methods. Prefer to use the async version, as this will
throw if there are unprocessed commands.

`typescript
const user = await userRepository.findById('123');
await user.register('123', 'Jeff');
await user.registerEmail('jeff@21jumpstreet.us');

// [ Event { type: 'user.registered.event' }, Event { type: 'user.email.registered.event' }]
const events = user.getUncommittedEvents();
`

#### getUncommittedEventsAsync

Retrieves the uncommitted events as soon as the processing queue is empty.

`typescript
const user = await userRepository.findById('123');
await user.register('123', 'Jeff');
await user.registerEmail('jeff@21jumpstreet.us');

// [ Event { type: 'user.registered.event' }, Event { type: 'user.email.registered.event' }]
const events = await user.getUncommittedEventsAsync();
`

#### getVersion

Retrieves the version of the aggregate, including increments for the processed uncommitted events.

`typescript
const user = await userRepository.findById('123');
// -1, non existing
const initialVersion = user.getVersion();

await user.register('123', 'Jeff');
await user.registerEmail('jeff@21jumpstreet.us');

// 2, set to 0 for initial + 2 increments for the events
const newVersion = user.getVersion();
`

$3

You will need to provide a Partition to the Repository.

#### checkConcurrencyStrategy

Checks the concurrency strategy provided in the Repository constructor. Returns a Promise with a boolean stating whether
it should throw an error or not. Defaults to resolving false if no concurrency strategy was provided.

Is used in the save method on the Repository in order to throw a concurrency error when there's a version
mismatch.

`typescript
const user = await userRepository.findById('123');
const initialVersion = user.getVersion();

await user.register('123', 'Jeff');
await user.registerEmail('jeff@21jumpstreet.us');

// 2, set to 0 for initial + 2 increments for the events
const newVersion = user.getVersion();
`

#### findById

Will look up an Aggregate in the Partition provided to the Repository by the aggregate's ID.

`typescript
const user = await userRepository.findById('123');
`

#### findByQueryStreamWithSnapshot

Will create a rehydrated aggregate by looking up the events for a stream, and processing them. Returns the rehydrated
aggregate.

Requires the persistence partition to implement queryStreamWithSnapshot.

`typescript
const user = await userRepository.findById('123');
`

#### findBySnapshot

Will look up a snapshot for the aggregate and Will create a rehydrated aggregate by looking up the events for a stream, and processing them. Returns the rehydrated
aggregate.

Requires the persistence partition to implement loadSnapshot & queryStream.

`typescript
const user = await userRepository.findById('123');
`

#### findEventsById

Retrieves the committed (processed) events for the aggregate stream by the aggregate's ID.

`typescript
// [{ type: 'user.registered.event' }. { type: 'user.email.registered.event' }]
const events = await userRepository.findEventsById('123');
`

#### save

Persists the aggregate including executed commands to the persistence partition.

`typescript
// { id: '123', contact: [] }
const user = await userRepository.findById('123');
await user.registerEmail('jeff@21jumpstreet.us');
await userRepository.save(user);

// { id: '123', contact: [{ value: 'jeff@21jumpstreet.us', type: 'email' }] }
const updatedUser = await userRepository.findById('123');
``