CQRS e Event Sourcing
CHE L'EVENTO SIA CON TE

ECCENTRIC DEVELOPER

Oscar Fanelli

Engineering Manager

Symfony / ZF / ReactJS

Team Management

Astronomia

JIRA / PhpStorm

Faccio cose

Conosco gente

Stringo mani

Pigio sulla tastiera

Troubles

  • How many customers bought an item after putting it in the basket?
  • How many users changed their mind about going to an event?
  • You are working on a banking application
  • 2 weeks ago you released a bug in production

more explosive example

APPLICATION

Event Storage

a whole new way to go crazy while coding

APPLICATION

ID NAME
4 Paul Red 50
ID NAME
4 Paul Red 250
ID NAME
4 Paul Red 200
ID NAME
4 Paul Red 120

APPLICATION

ID EVENT
4 Deposit 50
ID EVENT
4 Deposit 200
ID EVENT
4 Withdrawal 50
ID EVENT
4 Transfer 80

Targets

  • Reconstruct past states
  • Adjust current state to cope with retroactive changes (replay)
  • Complete rebuild

APPLICATION

MANAGER

EVENT STORAGE

event

EVENT
BUS

action

  • Reconstruct past states
  • Adjust current state to cope with retroactive changes (replay)
  • Complete rebuild
  • High-reliability

Targets

APPLICATION

EVENT STORAGE

PROVIDER

PROJECTOR 0

MANAGER

EVENT
BUS

PROJECTOR 1

PROJECTOR 2

PROJECTOR 3

EVENT STORAGE

Benefits

  • Event logging
  • Custom test environment (stop, rewind & replay)
  • Debugging
  • Seeds for new developers

Watch out

  • Events should have enough info to reverse them
  • External updates (third-party services) should be aware of a replay
  • External queries (es: exchange rate)
  • Lot of slow queries
  • Not easy to adopt

Auditing Bundle

only for lazy developers

APPLICATION

AUDITING
BUNDLE

EVENT STORAGE

event

EVENT
BUS

action

Auditing Bundle

  • Lighter version of the Event Sourcing 
  • Subscriber of:
    • Custom events
    • Entity events (CRUD)
    • Document events (CRUD)
  • Writes on the Event Storage whenever something happen
auditing_bundle:

    network: 'Your Application Name'

    whitelists:

        # entity lifecycles events that you want to whitelist (if empty, no entity lifecycle will be stored)
        # possible values: create|read|update|delete
        entity_lifecycles: [ "create", "read", "update", "delete" ]

        # document lifecycles events that you want to whitelist (if empty, no entity lifecycle will be stored)
        # possible values: create|read|update|delete
        document_lifecycles: [ "create", "read", "update", "delete" ]

        # custom objects that you want to audit (if empty, every object will be audited)
        objects: []

        # custom events that you want to audit (if empty, every custom event will be audited)
        events: []

    blacklists:

        # custom objects that you don't want to audit (if empty, every object will be audited)
        objects: []

        # custom events that you don't want to audit (if empty, every custom event will be audited)
        events: []

APPLICATION

AUDITING
BUNDLE

EVENT STORAGE

event

???

action

Who said CQRS?

Command Query Responsibility Segregation

CQRS

  • Perfect with Event Sourcing
  • Who reads data != who writes data
    • Provider
    • Manager
  • Helpful with business logic

Tips

  • Well-named event name (avoid update/inserted)
  • Events represent only what just happened
  • Events are immutable

In the end...

  • So much WOW!
  • You don't have to implement only this pattern
  • Don't use it if you don't need it

CQRS and Event Sourcing

SO LONG AND THANKS FOR ALL THE FISH.

oscar.fanelli@gmail.com

@nesis

OSCAR FANELLI

CQRS e Event Sourcing: che l'Evento sia con te

By Oscar Fanelli

CQRS e Event Sourcing: che l'Evento sia con te

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