CQRS & EventSourcing discovery

Workshop

Florent @florentpellet

Clément @clem_bouillier

Jean @jeanhelou

Emilien @ouarzy

Who are we ?

• 4 passionate guys initiated this workshop in 2015
• Feel free to give some feedback on GitHub

• 
  Clément
  @clem_bouillier
• 
  Emilien
  @ouarzy
• 
  Florent
  @florentpellet
• 
  Jean
  @jeanhelou

CQRS Concept

Ref. "Conceptual CQRS" - Alberto Brandolini

Event Sourcing Concept

NB: DecisionProjection is also called State

Ref. Jérémie Chassaing

The new unicorn

We’ll revolutionize the web!

We’ll create a product like Twitter but better ...

A revolution!

Mixter

Instead tweet...

we'll quack!

Event Storming mixter

Ref. "Event Storming" - Alberto Brandolini

Test Driven Workshop

• Working in pairs
• Execute "run" script and read instructions


• Red Test => Green Test


• 3 steps (+2 Bonus)
  • Command DeleteMessage
  • Query Timeline Message
  • Events in aggregate

Focus on Core Domain

• Do not change
  • Tests code
  • Infrastructure code


• You can see Identity context implementation as example

GIT Repository

git clone https://github.com/DevLyon/mixter.git

./run

Slide : http://devlyon.fr/mixter/

1. Delete Command

What we will learn :

• publish events from aggregate,
• use projection for decision inside aggregate (contains only "state" for future decision, DO NOT keep all state like in an entity)
• Implement "business rules" that insure aggregate consistency (based on decision projection and command=method parameters)

In brief : the C of CQRS

2. Timeline messages Projection

What we will learn :

• Create another model for Query (Projection, TimelineMessageProjection)
• Transform events in a projection model through an EventHandler
• A projection repository (in-memory) with its interface is given

In brief : Q of CQRS

3. Subscription Aggregate

What we will learn :

• Create a new aggregate (Subscription)
• Raise events from it : UserFollowed and UserUnfollowed
• Create a decision projection for it
• Implement replay of events (event sourced aggregate)

In brief : C of CQRS + Event Sourcing

4. Aggregates interaction

What we will learn :

• Coordinate several aggregates to limit coupling
• Concept of " Eventual consistency"

5. Command Handler

What we will learn :

• Integrate previous code from Message & Identity contexts in a command
• Write some web infrastructure code executing the command

=> Request Rest to execute delete Message command, with session validity verification
NB : no tests for this step for now…

CQRS & EventSourcing discovery

Thanks!

Florent @florentpellet

Clément @clem_bouillier

Jean @jeanhelou

Emilien @ouarzy