event sourcing · event sourcing lars vonk & bob forma in production systems tuesday, april 9,...
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Event sourcingLars vonk & Bob Forma
in production systems
Tuesday, April 9, 13
Let’s take a look how wecurrently develop software
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Tuesday, April 9, 13
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One model to rule them all
Repor&ng
Mix of concerns
QueryingTransac&ons (commands)
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How did this Invoice get to status :sent?
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How many items are deleted from the shopping cart just before an order is placed?
How did this Invoice get to status :sent?
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Information is lost
How many items are deleted from the shopping cart just before an order is placed?
How did this Invoice get to status :sent?
Tuesday, April 9, 13
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Event SourcingCapture all changes to an application state as a sequence of events
martinfowler.com/eeaDev/EventSourcing.html - Martin Fowler
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Or maybe not so different...
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Trivial exampleCurrent state
id amount status recipiented3456f 121 sent bob@zilverline.com
Tuesday, April 9, 13
Trivial exampleCurrent state
id amount status recipiented3456f 121 sent bob@zilverline.com
Event sourced
id event_type event_jsoned3456f InvoiceCreatedEvent {id:“ed3456f”}ed3456f LineItemAddedEvent {id:“ed3456f”, line_item: {id: 1, amount: 100, vat: 21}}ed3456f InvoiceSentEvent {id:“ed3456f”, to: “bob@zilverline.com”}
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Event sourced
id event_type event_jsoned3456f InvoiceCreatedEvent {id:“ed3456f”}ed3456f LineItemAddedEvent {id:“ed3456f”, line_item: {id: 1, amount: 100, vat: 21}}ed3456f LineItemRemovedEvent {id:“ed3456f”, line_item_id: 1}ed3456f LineItemAddedEvent {id:“ed3456f”, line_item: {id: 2, amount: 150, vat: 21}}ed3456f InvoiceSentEvent {id:“ed3456f”, to: “bob@zilverline.com”}
How many line items are deleted just before...
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So how do you query stuff?
The One Model To Rule Them All
CommandModel
Query Model
View
write
read
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So how do you query stuff?
CommandModel
Query Model
View
Tuesday, April 9, 13
So how do you query stuff?
CommandModel
Query Model
View
writere
ad
Tuesday, April 9, 13
So how do you query stuff?
CommandModel
Query Model
View
writere
ad
CQRS
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So how do you query stuff?
CommandModel
Query Model
View
write
‘generates using events’
read
CQRS
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Concrete example...
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User
Concrete example...
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User
POST /invoices/:id/send
Controller
Concrete example...
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User
POST /invoices/:id/send
Controller
SendInvoiceCommand
CommandHandler
Concrete example...
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User
POST /invoices/:id/send
Controller
SendInvoiceCommand
CommandHandler load_aggregate
Eventstore
Concrete example...
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User
POST /invoices/:id/send
Controller
SendInvoiceCommand
CommandHandler load_aggregate
Invoice
InvoiceCreatedEvent
LineItemAddedEventEventstore
load_from_history
Concrete example...
events are in past tense
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User
POST /invoices/:id/send
Controller
SendInvoiceCommand
CommandHandler load_aggregate
Invoice
InvoiceCreatedEvent
LineItemAddedEvent
send
Eventstore
load_from_history
InvoiceSentEvent
Concrete example...
events are in past tense
Tuesday, April 9, 13
User
POST /invoices/:id/send
Controller
SendInvoiceCommand
CommandHandler load_aggregate
Invoice
InvoiceCreatedEvent
LineItemAddedEvent
send
Eventstore
store
load_from_history
InvoiceSentEvent
Concrete example...
events are in past tense
Tuesday, April 9, 13
User
POST /invoices/:id/send
Controller
SendInvoiceCommand
CommandHandler load_aggregate
Invoice
InvoiceCreatedEvent
LineItemAddedEvent
send
Eventstore
store
load_from_history
publish_eventsEventHandler
InvoiceSentEvent
Concrete example...
events are in past tense
Tuesday, April 9, 13
User
POST /invoices/:id/send
Controller
SendInvoiceCommand
CommandHandler load_aggregate
Invoice
InvoiceCreatedEvent
LineItemAddedEvent
send
Eventstore
store
load_from_history
publish_eventsEventHandlerView
update
InvoiceSentEvent
Concrete example...
events are in past tense
Tuesday, April 9, 13
Part 1: For the business
Why Event Sourcing
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To capture user intent
Part 1: For the business
Why Event Sourcing
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To capture user intentHistoric informa&on
Part 1: For the business
Why Event Sourcing
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To capture user intentHistoric informa&onStorage decoupling
Part 1: For the business
Why Event Sourcing
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To capture user intentHistoric informa&onStorage decoupling
Part 1: For the business
Why Event Sourcing
Defer decisions
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Part 2: For us nerds
Why Event Sourcing
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Tell, don’t ask
Part 2: For us nerds
Why Event Sourcing
Tuesday, April 9, 13
Tell, don’t askIsolated domain tests
Part 2: For us nerds
Why Event Sourcing
Tuesday, April 9, 13
Tell, don’t askIsolated domain tests
Part 2: For us nerds
Why Event Sourcing
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Debug informa&on
Tell, don’t askIsolated domain tests
Part 2: For us nerds
Why Event Sourcing
Tuesday, April 9, 13
Debug informa&on
Tell, don’t askIsolated domain tests
Part 2: For us nerds
Conflict resolu&on
Why Event Sourcing
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It is not a Silver bullet
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Not for CRUD
It is not a Silver bullet
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Learning curve
Not for CRUD
It is not a Silver bullet
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Learning curve
Not for CRUD
More work to do simple stuff
It is not a Silver bullet
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Financial administra&on systemIntegrates with various systemsWeb-‐based
Case study Freemle.com
Event source approved
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THE INTERNALS
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Stack
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Domain
Invoice
Organization
ExpenseCustomer
Bank
Invoice numbers
Ledger
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User
POST /invoices/:id/send
Controller
SendInvoiceCommand
CommandHandler load_aggregate
Invoice
InvoiceCreatedEvent
LineItemAddedEvent
send
Eventstore
store
load_from_history
publish_eventsEventHandlerView
update
InvoiceSentEvent
events are in past tense
Remember this picture?
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User wants to mark an invoice as paid
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Request is translated to specific command
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Propagates to correct Domain object
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Retrieves all events for Aggregate
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What does an event look like?
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Rebuild yourself from history
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Events are applied
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Propagates to correct Domain object
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Tell the invoice it has been paid
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Apply events on yourself
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Update your state
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Commit the events in the EventStore
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Publish the events to registered Handlers
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Update view model
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Render view
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User
POST /invoices/:id/send
Controller
SendInvoiceCommand
CommandHandler load_aggregate
Invoice
InvoiceCreatedEvent
LineItemAddedEvent
send
Eventstore
store
load_from_history
publish_eventsEventHandlerView
update
InvoiceSentEvent
events are in past tense
Summary
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EXAMPLE HISTORIC INTEL
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Introducing the timeline
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What was easy?
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Querying (separate model)
What was easy?
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Querying (separate model)Implemen&ng business logic
What was easy?
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Querying (separate model)Implemen&ng business logicMeasuring feature usage
What was easy?
Tuesday, April 9, 13
Querying (separate model)Implemen&ng business logicMeasuring feature usage
What was easy?
Read performance (op&mized view model)
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Querying (separate model)Implemen&ng business logicMeasuring feature usage
What was easy?
Read performance (op&mized view model)No BDUF for the data model
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What was hard?
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What was hard?Mental model change (thinking in events)
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Event upcas&ng
What was hard?Mental model change (thinking in events)
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Defining events
Event upcas&ng
What was hard?Mental model change (thinking in events)
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Open challenges
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Open challenges
Replay all events performance
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Open challenges
Replay all events performanceReplay all events performance
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Asynchronous view model update
Open challenges
Replay all events performanceReplay all events performance
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Zero down&me deployments
Asynchronous view model update
Open challenges
Replay all events performanceReplay all events performance
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Zero down&me deployments
Scaling
Asynchronous view model update
Open challenges
Replay all events performanceReplay all events performance
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Questions?
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