1 Understanding and Applying CQRS Vinicius Feitosa Pacheco @ViniciusPach 07.23.18
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1
Understanding andApplying CQRS
Vinicius Feitosa Pacheco
@ViniciusPach
07.23.18
2
Microservice Patterns and Best PracticesVinicius Feitosa PachecoJanuary 2018
http://bit.ly/microservice-book
@ViniciusPach
Agenda
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1. What is CQRS?
2. When can we use CQRS ?
3. Understanding CQRS
4. Applying CQRS
5. Common Mistakes
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What is CQRS?1
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Command
Query
Responsibility
Segregation
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CQRS is simply the creation of two objects where there was previously only one. The separation occurs based upon whether the methods are a command or a query...
Young, Greg (2010)
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When can we use CQRS ?2
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The “Normal” Architecture
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UI / API
Domain
Repository
Model
DB
Read Write
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App InstanceApp Instance App Instance App InstanceApp Instance
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First possible solution: Master/Slave
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UI / API
Domain
Repository
Model
Master SlaveSlave
Read Write
Eventual Consistency
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Second possible solution: Cache
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UI / API
Domain
Repository
Model
MasterCache
WriteRead
Data Synchronization
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When CQRS is util?
● When my storage is a bottleneck.
● When the application has complex queries and these
queries could be optimized.
● When a big number of users are updating a small data
set and the data could be outdated.
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Understanding CQRS3
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CQRS
● Query Stack – Operations that retrieve information from
the data in the application.
● Command Stack – Operations that modify the State of
the data in the application.
QueryStack
3.1
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QueryStack
● It is simpler than the CommandStack.
● It is a synchronous layer that retrieves data from a
denormalized reading.
● Presumes “flat” queries.
CommandStack
3.2
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CommandStack
● Potentially asynchronous.
● Has behavior-centric approach where all business intention is initially triggered by the
client as a use case.
● The Commands are declared in an imperative fashion and are raised
asynchronously.
● The handlers returns success or failure.
● A command updates the state of an entity and raises an event that will update the
data needed in the database reading.
Synchronization
3.3
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Synchronization: Automatic updating
QueryStack
CommandStack
GET
POST/PUT...
Synchronous(REST/RPC...)
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Synchronization: Update possible
QueryStack
CommandStack
GET
POST/PUT...
Asynchronous(Bus/Queues...)Event
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Synchronization: Controlled update
QueryStack
CommandStack
GET
POST/PUT...
Asynchronous(Cron Process...)
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Synchronization: Update on demand
QueryStack
CommandStack
GET
POST/PUT... A
B
Asynchronous(Check-in Process)<
Queueing
3.4
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Applying CQRS4
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https://github.com/viniciusfeitosa/europython2018
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Common Mistakes5
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Mistake 1:
CQRS and Event Sourcing must be
implemented together
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Mistake 2:
CQRS requires eventual consistency
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Mistake 3:
CQRS depends on Queues and Message
Brokers
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Mistake 4:
CQRS is easy
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Mistake 5:
CQRS is architecture
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CQRS is the best thing since sliced bread!
Pacheco, Vinicius (Today)
40
Microservice Patterns and Best PracticesVinicius Feitosa PachecoJanuary 2018
http://bit.ly/microservice-book
@ViniciusPach
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May the CQRS be with you
Kenobi, Vinicius (2018)
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Thank you
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