Quickstart

Install

npm i --save serverless-cqrs
npm i --save serverless-cqrs.memory-adapter

Usage

To start, you need Actions and a Reducer. So let's write simple ones:

actions.js
const actions = {
addTodo: (state, payload) => {
if (!payload.title) throw new Error('titleMissing')
return [{
type: 'TodoAdded',
title: payload.title,
at: Date.now(),
}]
}
}
module.exports = actions
reducer.js
const initialState = {
todos: []
}
const reducer = (state, event) => {
switch (event.type) {
case 'TodoAdded':
return {
todos: [
...state.todos,
{ title: event.title },
]
}
default:
return state
}
}
module.exports = (events, state=initialState) => events.reduce(reducer, state)

Above we have a basic action and reducer.

  • The action ,addTodo, does some basic validation to check the presence of a title and if it succeeds, returns a new event with the type TodoAdded.

  • When that event is run through the reducer, a new todo is appended to the list.

Next, we build an adapter to help us persist the events.

adapter.js
const memoryAdapterBuilder = require('serverless-cqrs.memory-adapter')
module.exports = memoryAdapterBuilder.build({
entityName: 'todo'
})

This adapter will let us persist events and read-model projections in memory.

Finally, we use these to build our read and write model.

app.js
const {
writeModelBuilder,
readModelBuilder,
} = require('serverless-cqrs')
const actions = require('./actions')
const reducer = require('./reducer')
const adapter = require('./adapter')
module.exports.writeModel = writeModelBuilder.build({
actions,
reducer,
adapter,
})
module.exports.readModel = readModelBuilder.build({
reducer,
adapter,
eventAdapter: adapter,
})

That's it!

Try it live