event sourcing the best ubiquitous pattern you have never heard off

Event Sourcing :The Best Ubiquitous Pattern You've Never Heard Of

Joe Drumgoole

Director of Developer Advocacy, EMEA@jdrumgoole

V1.1

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Event Sourcing – not a new idea

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Our Relational Friends Love It

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We do It Ourselves

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Think of a File backup system

Source Disk

Backup Disk

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Trivial Backup

Source Disk

Backup DiskMyFile.jpg

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But…

Source Disk

Backup DiskMyFile.jpg

MyFile.jpg

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Lets Use a Backup Tool

Source Disk

Backup DiskMyFile.jpg

MyFile.jpg

Admin

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What if We are a SaaS Backup Company?

MyFile.jpg MyFile.jpg

MyFile.jpg

MyFile.jpg

MyFile.jpg

AuditMyFile.jpg

MyFile.jpgMyFile.jpg

MyFile.jpgMyFile.jpg

MyFile.jpg

MyFile.jpg

MyFile.jpgMyFile.jpg

MyFile.jpgMyFile.jpg

MyFile.jpgMyFile.jpg

MyFile.jpg

Audit

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What real SaaS Backup Companies do

Event 1MyFile.jpg

Event 2

Event 3

Event 4

Event 5

Event N

MyFile.jpg Start

MyFile.jpg End

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Where else is this Useful?

How Did I Get Here?

What's in the Box?

An Immutable Append Only Log

Snapshots for point in time state

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Where Do Events Come From?

Commands

Root Aggregate

Business Events

Aggregate Value

AggregateValue

Event 1

Event 2

Event 3

Event 4

Event 5

Event 6

Event 7

Event 8

Event 9

Event N

Event N + 1

Snapshots for point in time state

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Some Example Snapshot Queries

• What POs failed to get approved in Q2?• Which cabs billed more than $50 a journey?• Which cabs get the biggest tips?• How many baskets have had $200 for two weeks or more?• Which sensor events exceeded the safety threshold on 21-July-

2016?

CQS

CQRS

Command Query Segregation

Command Query Responsibility Segregation

Begat

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Split the ResponsibilitiesCommands

CommandsCommands

CommandsCommands

Commands

Domain Objects

EventsEvents

EventsEvents

EventsEvents

EventsEvents

Domain Objects

CommandsCommands

CommandsCommands

CommandsQueries

Query ObjectsQuery Objects

Domain Data

Snapshot

Snapshot

Snapshot

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In MongoDB SpeakDomain Objects Query Objects

Query Objects

P

S S

Domain Objects

Replica Set/Sharded Cluster Query Cluster

P

S S

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Domain Object - Eventpurchase_order = { "ID" : "1222-344-27", "timestamp" : "Wed Oct 19 2016 16:50:27 GMT" "dept" : "Manufacturing", "Purchase From" : { "company" : "ABC Ltd", "company number" : 12345678, "VAT ID" : "773456K", "Address" : { ... } } "line items" : [ { ... }, { ... } ], "VAT" : 540.0 "total price" : 2567.54 "currency" : "Euro", "Supplier Ref" : "YF-27-567", "delivery address" : { ...} }

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Summary

• Event Sourcing : Capture the state as first class objects• CQRS : Optimise differently for commands and queries• MongoDB ideally suited to build both event store and query store• Use different storage engines depending on use case• The aggregation framework generates summary data