ECCENTRIC DEVELOPER

Oscar Fanelli

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

APPLICATION

APPLICATION

Targets

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

APPLICATION

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

Targets

APPLICATION

EVENT STORAGE

MANAGER

EVENT
BUS

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

APPLICATION

EVENT STORAGE

EVENT
BUS

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

???

Who said CQRS?

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