Rethink your architecture with CQRS
60
Rethink your architecture with CQRS Pieter Joost van de Sande Passionated software developer, Atos Email: [email protected] @twitter: pjvds
description
Rethink your architecture with CQRS. Pieter Joost van de Sande Passionated software developer , Atos. E mail: [email protected] @ twitter : pjvds. This is meant to be a take away!. Architecture. Architecture. Presentation. Domain. Data. Presentation. Why do we love it?. Domain. - PowerPoint PPT Presentation
Transcript of Rethink your architecture with CQRS
Rethink your architecturewith CQRS
Pieter Joost van de SandePassionated software developer, Atos
Email: [email protected]@twitter: pjvds
This is meant to be a take away!
Architecture
Architecture
Presentation
Domain
Data
Presentation
Domain
Data
Why do we love it?
model
Domain Driven DesignEric Evans - 2003
The value of a structured Model
Who believes in this?
Structured models are always created from a single viewpoint!
A model can only be optimized for one thing… and one thing only!
Presentation layer
Data layer
Domain layerSend DTO
Send DTO
Map DTO
Map DTO
Write data Write data
Map DTO
Write data Write data
Send DTO
Request DTO
Map DTO
RequestDTO
Map DTO
Query data Query data
Request data
Map DTO
Query data Query data
RequestDTO
Send updateUpdate screen
TWO FUNDAMENTALS
Information
Transitions
WRITING != READING
From 3-tier to CQRS
Presentation layer
Domain layer
Data layer
Presentation layer
Domain layerData layer
Just re-order the tiers
Presentation layer
Domain layerData layer
Switch dependency
Presentation layer
Domain layerData layer
CQRS!
Query side Command side
FROM CONCEPT TO ARCHITECTURE
HERE WE GO!
User interface
Demand for information
User interface
Read side
We read a lot
We have multiple screens to fill
Data should be close to us
Relational databases are sub optimal for view data!
SELECT CCUS.CUST_FIRST_NAME , CCUS.CUST_LAST_NAME , CINT.CUST_INTEREST_RANK , CILO.CUST_INTERSTFROM CUST_CUSTOMER AS CCUS , CUST_INTEREST_LOOKUP AS CILO , CUST_INTEREST AS CINTWHERE ( CCUS.CUST_CITY = 'Singapore' AND CCUS.CUST_PROV_STATE = 'Singapore' AND CCUS.CUST_CODE IN ( SELECT COHE.CUST_CODE FROM CUST_ORDER_HEADER AS COHE , CUST_ORDER_STATUS AS COST WHERE ( COHE.CUST_ORDER_DATE >='2009-01-01 00:00:00.001' AND COST.CUST_ORDER_STATUS IN( 'Shipped', 'Back-ordered', 'In-process' ) AND COHE.CUST_ORDER_STATUS_CODE = COST.CUST_ORDER_STATUS_CODE ) ) AND CCUS.CUST_CODE = CINT.CUST_CODE AND CINT.CUST_INTEREST_CODE = CILO.CUST_INTEREST_CODE )ORDER BY CCUS.CUST_LAST_NAME ASC , CCUS.CUST_FIRST_NAME ASC , CINT.CUST_INTEREST_RANK ASC
Evil execution plan!
Bottom line
• Getting data should be simple – select * from x where y
• Examples:– Get all products of user X– Get total price of all orders of month May
User interface
Read side
Read side
User interface
Read databases
Read side
User interface
Read databases
Facade
Read side
User interface
Facade
Read databases
DTO’s
Demand for change
I want to tell the system something
Read side
User interface
Facade
Read databases
DTO’s
Write side
User interface
Commandhandlers
Read databases
Read side
commands DTO’s
Write side
Facade
Commands• Simple message contains all info needed• Lower coupling (law of demeter)• Causes a state transition• Contains the intend of the user• Exists in a bounded context
• Examples:– AddProductToShoppingCart– PurchaseOrder– MoveUserToNewAddress– CorrectAddressForUser– FinalizeOrder
Commands example
Create Cart
Add item
Add item
Add item
Remove item
Purchase
Users don’t make changes for nothing, intent is important!
Change has intent
• Users don’t make changes for nothing• This intent has value!
Correct the address for
user X
Customer X moved to
new addressVS.
User interface
Commandhandlers
Read databases
Read side
commands DTO’s
Write side
Facade
User interface
Commandhandlers
Read databases
Read side
commands DTO’s
Dom
ein
Write side
Repository
Facade
Event Sourcing
Events
• Simple message that describes an event• Contains intent• Contains all the data related to the event• Past tense
CustomerMoved{
CustomerId,NewAddress
}
Transitional flow
User interface
Commandhandlers
Read databases
Read side
commands DTO’s
Dom
ein
Write side
Repository
Facade
User interface
Commandhandlers
Read databases
Read side
commands DTO’s
Dom
ein
Write side
Repository
Facade
Event store
• Contains all domain events• Does not need to be relational• Write are *awesomely* fast!• Rock solid audit log• Read models can (re)build themself of it• The domain uses it to get the current state
• Can be used to build any structural model you want!
User interface
Commandhandlers
Read databases
Read side
commands DTO’s
Dom
ein
Write side
Repository
?
Facade
User interface
Commandhandlers
Repository
Event bus
Read databases
Write side Read side
eventscommands DTO’s
Dom
ein
Facade
User interface
Commandhandlers
Repository
Event bus
Deno
rmal
izers
Read databases
Write side Read side
events
events events
commands DTO’s
Dom
ein
Facade
Application flow
Wrap up
• Optimize for reading and writing• Makes changes part of the problem domain• Free rock solid audit log• Capture the intent of changes• Allow multiple read models
Thank you!You’ve been a great audience!
