CQRS and Event Sourcing
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The document discusses CQRS (Command Query Responsibility Segregation) and Event Sourcing application architectures. It begins with an overview of common application architectures like layered architecture and hexagonal architecture. It then explains event-driven architecture and how event sourcing can be used for data storage. CQRS is introduced as separating read and write interfaces. The document contrasts a traditional architecture with one using CQRS and event sourcing together. It provides a code example and concludes with questions and resources for further reading.
![Source:
[Evans,
DDD]
Layered Architecture
• One
of
the
oldest
paGerns
• Each
layer
could
couple
only
to
itself
or
below
• Lower
levels
could
loosely
couple
to
upper
via
Observer
or
Mediator
[GoF]
• UI
Layer
– Only
renders
informa0on
– Example:
OHS
(Remote
Façade)
• Applica0on
Layer
– Very
lightweight
– Building
Blocks:
Applica0on
Services
– Coordinate
opera0ons
over
Aggregates
(i.e.
express
Use
Cases)
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 4](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-4-320.jpg)
![Source:
[Evans,
DDD]
Layered Architecture
• Applica0on
Layer
– Register
Subscribers
for
Dom.
Events
– Transac0ons,
Email
sending
etc.
– Devoid
of
domain
logic
• Domain
Layer
– Expressive
Behavioural-‐Rich
Domain
Model
• Infrastructure
Layer
– Low
Level
Services
– Focus
on
technology
specific
decisions
– Persistence,
Messaging,
etc.
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 5](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-5-320.jpg)
![Source:
[Vernon,
DDD]
Hexagonal Architecture (HA)
• Also
known
as
“Ports
and
Adapters”
• Ports
– Outer
hexagon
(HTTP,
Messaging
etc.)
– Each
hexagon’s
side
represents
a
port
– Either
for
input
or
output
– Do
not
implement
ports(use
e.g.
Jersey)
• Adapters
– Transform
client’s
input
into
internal
API’s
“terms”
– Transform
internal
API’s
output
to
input
suitable
for
clients
– Each
client
type
has
an
Adapter
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 6](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-6-320.jpg)
![Source:
[Vernon,
DDD]
Hexagonal Architecture (HA)
• Outer
hexagon
reaches
inner
hexagon
via
applica0on’s
API
• Design
applica0on
inside
per
func0onal
requirements(use
cases
API)
• Layered
Architecture
+
DI
encourages
the
use
of
Hexagonal
Arch.
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 7](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-7-320.jpg)
![Event Driven Architecture (EDA)
• EDA
could
be
combined
with
Hexagonal
Architecture
(HA)
– EDA
used
for
integra0on
– HA
used
for
Bounded
Contexts
– LA
could
replace
HA
as
well
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 9
Source:
[Vernon,
DDD]](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-9-320.jpg)
![Event Driven Architecture (EDA)
• Events
as
mechanism
for
Storage
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 10
Source:
[Vernon,
DDD]](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-10-320.jpg)
![CQRS
• Stereotypical
vs.
CQRS
Architecture
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 13
Source:
[Young,
CQRS]
Stereotypical Architecture](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-13-320.jpg)
![CQRS
• Stereotypical
vs.
CQRS
Architecture
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 14
Source:
[Young,
CQRS]
CQRS](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-14-320.jpg)
![Source:
[Young,
CQRS]
CQRS + ES
• CQRS
+
EDA
with
Domain
Events
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 16](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-16-320.jpg)
![CQRS + ES
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 17
Source:
[Young,
CQRS]](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-17-320.jpg)
![Resources
• [Evans,
DDD]
"Domain-‐Driven
Design:
Tackling
Complexity
in
the
Heart
of
Sonware",
Eric
Evans,
Addison
Wesley,
20/08/2003,
ISBN:
0-‐321-‐12521-‐5
• [Vernon,
DDD],
"Implemen0ng
Domain-‐Driven
Design",
Vaughn
Vernon,
2013,
ISBN-‐10:
0-‐321-‐83457-‐7,
ISBN-‐13:
978-‐0-‐321-‐83457-‐7
• [Young,
CQRS],
"CQRS
Documents
by
Greg
Young",
Greg
Young,
11/2010.
hGp://
cqrs.files.wordpress.com/2010/11/cqrs_documents.pdf
• [Cockburn,
Hex
Arch]
"Hexagonal
Architecture",
h"p://alistair.cockburn.us/Hexagonal
+architecture
• [Fowler,
NoSQL
talk]
"NoSQL
maGers
Cologne
2013
-‐
Key
Note:
NoSQL
Dis0lled
to
an
hour
-‐
Mar0n
Fowler",
Mar0n
Fowler,
2013,
h"p://vimeo.com/66052102
• Domain
Driven
Design
Website,
h"p://domaindrivendesign.org/
• DDD
User
Group,
h"p://tech.groups.yahoo.com/group/domaindrivendesign/
• DDD
Community,
h"p://dddcommunity.org/
• CQRS
Official
Website,
h"p://cqrs.wordpress.com/
Bulgarian Java User Group
Nikolay Vasilev, CC BY-SA 3.0
CQRS + ES Page 23](https://image.slidesharecdn.com/cqrs-and-es-bg-jug-v-150904064806-lva1-app6892/85/CQRS-and-Event-Sourcing-23-320.jpg)
CQRS and Event Sourcing
- 1. CQRS and Event Sourcing Nikolay Vasilev
- 2. CQRS and Event Sourcing • Applica0on Architecture • CQRS and Event Sourcing • Code / Example • Ques0ons • Resources Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 2
- 3. Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 Application Architecture
- 4. Source: [Evans, DDD] Layered Architecture • One of the oldest paGerns • Each layer could couple only to itself or below • Lower levels could loosely couple to upper via Observer or Mediator [GoF] • UI Layer – Only renders informa0on – Example: OHS (Remote Façade) • Applica0on Layer – Very lightweight – Building Blocks: Applica0on Services – Coordinate opera0ons over Aggregates (i.e. express Use Cases) Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 4
- 5. Source: [Evans, DDD] Layered Architecture • Applica0on Layer – Register Subscribers for Dom. Events – Transac0ons, Email sending etc. – Devoid of domain logic • Domain Layer – Expressive Behavioural-‐Rich Domain Model • Infrastructure Layer – Low Level Services – Focus on technology specific decisions – Persistence, Messaging, etc. Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 5
- 6. Source: [Vernon, DDD] Hexagonal Architecture (HA) • Also known as “Ports and Adapters” • Ports – Outer hexagon (HTTP, Messaging etc.) – Each hexagon’s side represents a port – Either for input or output – Do not implement ports(use e.g. Jersey) • Adapters – Transform client’s input into internal API’s “terms” – Transform internal API’s output to input suitable for clients – Each client type has an Adapter Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 6
- 7. Source: [Vernon, DDD] Hexagonal Architecture (HA) • Outer hexagon reaches inner hexagon via applica0on’s API • Design applica0on inside per func0onal requirements(use cases API) • Layered Architecture + DI encourages the use of Hexagonal Arch. Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 7
- 8. Event Driven Architecture (EDA) • Event Sourcing • Promotes, detect, consume and react to events • Pipes and Filters Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 8 EpisodeAdded b#1,s#2 SeriesRenamed b#20,s#1 BrandAc0vated b#3
- 9. Event Driven Architecture (EDA) • EDA could be combined with Hexagonal Architecture (HA) – EDA used for integra0on – HA used for Bounded Contexts – LA could replace HA as well Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 9 Source: [Vernon, DDD]
- 10. Event Driven Architecture (EDA) • Events as mechanism for Storage Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 10 Source: [Vernon, DDD]
- 11. Event Driven Architecture (EDA) • Append-‐only architecture – No “Delete” ac0on • Distribute easier than RDBMS – Due to no locks – Sharding (uses only Aggregate keys) • Loading Objects – Loads accumulated events for an Aggregate – Performance issue for over than 100 events – Rolling Snapshots Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 11 EpisodeAdded b#1,s#2 SeriesRenamed b#20,s#1 SeriesRemoved b#10,s#2 BrandAc0vated b#3 4 3 snap 2 1
- 12. CQRS • Command and Query Responsibility Segrega0on (CQRS) • Bertrand Mayer’s CQS Principle – Command: If method alters the state should not return value (i.e. returns void) – Query: If you return value you cannot mutate state • What if we apply it at architectural level? ;) Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 12 Read Service Write Service
- 13. CQRS • Stereotypical vs. CQRS Architecture Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 13 Source: [Young, CQRS] Stereotypical Architecture
- 14. CQRS • Stereotypical vs. CQRS Architecture Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 14 Source: [Young, CQRS] CQRS
- 15. CQRS and Event Sourcing Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0
- 16. Source: [Young, CQRS] CQRS + ES • CQRS + EDA with Domain Events Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 16
- 17. CQRS + ES Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 17 Source: [Young, CQRS]
- 18. Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 Code / Example
- 19. Code / Example • Example project – DDD-‐CQRS Sample, (v.02) – HLA: h"p://prezi.com/akrfq7jyau8w/ddd-‐cqrs-‐leaven-‐v20/ – Code base: h"ps://github.com/Bo"egaIT/ddd-‐leaven-‐v2 – User Group: h"ps://groups.google.com/forum/#!forum/ddd-‐cqrs-‐sample • More projects on official CQRS site – hGp://cqrs.wordpress.com/examples/ Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 19
- 20. Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 Questions?
- 21. Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 21 Thank you for your aGen0on!
- 22. Resources
- 23. Resources • [Evans, DDD] "Domain-‐Driven Design: Tackling Complexity in the Heart of Sonware", Eric Evans, Addison Wesley, 20/08/2003, ISBN: 0-‐321-‐12521-‐5 • [Vernon, DDD], "Implemen0ng Domain-‐Driven Design", Vaughn Vernon, 2013, ISBN-‐10: 0-‐321-‐83457-‐7, ISBN-‐13: 978-‐0-‐321-‐83457-‐7 • [Young, CQRS], "CQRS Documents by Greg Young", Greg Young, 11/2010. hGp:// cqrs.files.wordpress.com/2010/11/cqrs_documents.pdf • [Cockburn, Hex Arch] "Hexagonal Architecture", h"p://alistair.cockburn.us/Hexagonal +architecture • [Fowler, NoSQL talk] "NoSQL maGers Cologne 2013 -‐ Key Note: NoSQL Dis0lled to an hour -‐ Mar0n Fowler", Mar0n Fowler, 2013, h"p://vimeo.com/66052102 • Domain Driven Design Website, h"p://domaindrivendesign.org/ • DDD User Group, h"p://tech.groups.yahoo.com/group/domaindrivendesign/ • DDD Community, h"p://dddcommunity.org/ • CQRS Official Website, h"p://cqrs.wordpress.com/ Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 23
- 24. Bulgarian Java User Group Nikolay Vasilev, CC BY-SA 3.0 CQRS + ES Page 24