applying cqrs and event sourcing in .net...
TRANSCRIPT
Applying CQRS and Event
Sourcing in .NET applications
Dino Esposito
JetBrains
@despos
facebook.com/naa4e
WARNINGThis is NOT simply a shameless plug
but a truly helpful reference
“I will say that in a number of cases, a page
from this book erased a mass of confusion I'd
acquired from Vaughn Vernon's Implementing
Domain-Driven Design. This was written in a
much more concise, clear, practical manner
than that book.”
—(non anonymous) Amazon reviewer
http://naa4e.codeplex.com
IITYWIMWYBMAD?
CQRS
If I Tell You What It Means Will You Buy Me A Drink?
2G2BT AGKWE KUTGW WTHIN?
One
Comprehensive
Software Model
for the Business
Domain
Query
Returns data
Doesn’t alter
state
Command
Alter state
Doesn’t
return data
Separation
Responsibility
Bertrand Meyer called it
Command/Query Separation back in the 1980s
ONE BIG ISSUE LEADING TO CQRS
How to design a single model to address of all
aspects and concerns of a business domain?
How to do that effectively?
Theory
Begin End
Practice
Relevant data
Relevant tasks
WHERE DOES COMPLEXITY COME FROM?
Relevant data tables
Relevant tasks
WHERE DOES MORE COMPLEXITY COME FROM?
even more
Presentation layer
Application layer
Infrastructure layer
Canonical layered architecture
Domain layer
Presentation layer
Application layer
Infrastructure layer
CQRS
Commands Queries
Domain layer
Data
access
+
DTO
O(C x Q) vs. O(C + Q)
ONE BIG ISSUE LEADING TO CQRS
We faced a lot of complexity in modeling and
we thought it was inherent domain complexity
BenefitsSimplification of the design
Potential for enhanced scalability
Side effectsEasier to
maintain and evolve stacks
Optimize each stack
separately
ASPECTS OF CQRS
BUSINESS
DOMAIN
Command
Context #1
Query
Context #1
Command
Context #2
Query
Context #2
Command
Context #3
Query
Context #3
CQRS Design
DDD Analysis
CONTEXT
#1
CONTEXT
#2
CONTEXT
#3
Requirements
FLAVORS OF CQRS
• TX Script
• Your choice of DAL
• Shared DB
Regular
• Aggregates
• Your choice of DAL
• Data DB + snapshots
Premium
• Event-driven architecture
• LET or any choice of DAL
• Data DB + snapshots + event storeDeluxe
REGULAR CQRS
PRESENTATION
TX SCRIPT TX SCRIPT
APPLICATION APPLICATION
DAL
Simply use s-procs to
read or ADO.NET or EF
or whatever else suits
you. Just use DTO to
bring data back.
PREMIUM CQRS
PRESENTATION
DOMAIN LAYER
APPLICATION APPLICATION
DAL
Business logic
implemented through
aggregates and
domain model. State
of aggregates also
persisted in a format
suitable for the UI.
Sync
DELUXE CQRS
PRESENTATION
EVENT-DRIVEN BIZ
APPLICATION APPLICATION
DAL
Business logic
implemented through
aggregates and
domain model. State
of aggregates also
persisted in a format
suitable for the UI.
Sync
DELUXE CQRS
APPLICATIONApplication logic
expressed through
commands pushed to
a bus generating
events handled by
sagas (stateful) and
handlers (stateless).
Optionally events
recorded to a log.
Sync
DOMAIN LAYER Event
store
QUERY
STACK
…Saga(s) Handler(s)
BUS
DEMO
AT THE VERY END OF THE DAY
CQRS brings just one core idea: keep write and read stacks completely separated and based on different models and even different implementation patterns and technologies.
Best-selling point of CQRS is that it looks like common sense and a smarter way of doing just the same things.
CQRS is not a philosophy or a methodology:
it's just about writing code.
FOLLOW
Thank You!
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