Event sourcing
@JakubPilimon
jakub.pilimon@gmail.com
github.com/pilloPl
ORM
STATE
STATE
new ShopItem("ordered")item.setStatus("paid")...insert into shop_items (id, status) values (1, 'ordered')update shop_items set status = 'paid' where id = 1...
"new instance of ordered Shop Item was created"
"this shop item was marked as paid"...new ItemOrdered(itemID, timestamp)
new ItemPaid(itemID, timestamp)
item.setStatus("paid")new ShopItem("ordered")new ShopItem("ordered")ordered.setStatus("paid")State 1
State 2
(State 1 + Event 2)
single ShopItem deltas
technology agnostic log, descriptive event log
@Entity
class Product {
private float price;
//...
public void cutPrice(int percent) {
checkState(percent < 100);
this.price =
price - price * percent / 100;
DomainEvents.publish(
new NewPriceAssigned(percent, this.id));
}
} def 'should cut price by 10 percent'() {
given:
ShopItem item = newWithPrice(50.00)
when:
item.cutPrice(10)
then:
item.price == 45.00
} def 'should cut price by procent'() {
given:
ShopItem item = newWithPrice(50)
when:
item.cutPrice(10)
then:
item.getUncommittedChanges() ==
[new NewPriceAssigned(price: 45)]
}QUERIES
message broker
Shop
UI
Horizontal asymmetric scaling
Failover
A/B testing
&
blue green deployments
Partitioning
Adding new service
message broker
Shop
UI
Orders
Manager
Shipping
Performance
Testing?
Shop
(write model)
UI (read model)
eventually events
commands
DTOs
front end
Pitfalls
Replaying with side effect
calling SMS service
Event handler
IDEMPOTENCY
Replaying with side effect
SmsRequested
Event handler
calling SMS service
deleting SmsRequested
no 2PC
Process manager
new SmsRequested(uuid)
Event handler
calling SMS service
new SmsSent(uuid)
event store
@StreamListener(Sink.INPUT)
public void commandStream(Event event) {
//...saveSomething and changeState
}
//not run when replying!!!
@AfterAcknowledging(Sink.INPUT)
public Consumer<Event> doNext(Event event) {
return event -> ...
}Thank you!
@JakubPilimon
jakub.pilimon@gmail.com
github.com/pilloPl
Event sourcing
By Jakub Pilo
Event sourcing
Overview of event sourcing and CQRS benefits
