CQRS

… AND EVENT SOURCING

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CQRS EVENT SOURCING

… AND CQRS … AND EVENT SOURCING

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IN LAYMAN’S TERMS:

IT’S ALL ABOUT HANDLING MAKING CHANGES (TO THE DATABASE)

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HOW CHANGE LOOKS LIKE

STATE A

STATE B!

"

!

MUTATE

#READ

$WRITE

DATABASET R A N S I T I O N

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PROBLEMS OF STANDARD APPROACH

WHAT WAS THE A STATE? HOW ENTITY CHANGES OVER TIME?

WHO MADE THE TRANSITION? WHO WAS ENVOLVED IN MAKING CHANGES TO ENTITY OVER TIME?

WHEN WAS THE TRANSITION MADE?HOW MANY TIMES ENTITY CHANGED?

WHAT HAS ACTUALLY HAPPENED?WHAT WERE THE TRANSITIONS OVER TIME AND WHY THEY HAPPENED?

WHAT WOULD WE NORMALLY DO?

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LOG CHANGES IN SEPARATE TABLE(S)

"

STATE A

STATE B

!

!

&

ENTITIES

CHANGESMUTATE&

& &

& &#

READ

$WRITE

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PROBLEMS OF LOGGING CHANGES ONLY

WE STILL DON’T KNOW WHAT HAS HAPPENED WE KNOW TRANSITIONS … BUT WHAT ARE THE INTENTS?

WHAT PART OF THE SYSTEM MADE THE CHANGE?WAS IT A HUMAN OR AN AUTOMATED SYSTEM (WHICH ONE)?

WHAT WAS THE MUTATION? STORING MUTATION AND STATE IS REDUNDANT

WHAT HAPPENS WHEN DELETING AN ENTITY? SHOULD WE DELETE LOGS TOO?

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EVENT SOURCING TO THE RESCUE!

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LET’S RECOGNISE THINGS

ENTITY

INTENT / TRANSITION

MUTATION

“STANDARD APPROACH” EVENT SOURCING

AGGREGATE CACHED STATE#

EVENT#

EVENT DATA#

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EVENT SOURCING

"

STATE A

STATE B

!

!

ENTITIES

MUTATE&#

READ

$WRITE

EVENTS

&& &

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RECAP: PROBLEMS OF STANDARD APPROACH

WHAT WAS THE A STATE? HOW ENTITY CHANGES OVER TIME?

WHO MADE THE TRANSITION?WHO WAS ENVOLVED IN MAKING CHANGES TO ENTITY OVER TIME?

WHEN WAS THE TRANSITION MADE?HOW MANY TIMES ENTITY CHANGED?

WHAT HAS ACTUALLY HAPPENED?WHAT WERE THE TRANSITIONS OVER TIME AND WHY THEY HAPPENED?

SOLVED

SOLVED

SOLVED

SOLVED

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RECAP: PROBLEMS OF LOGGING CHANGES ONLY

WE STILL DON’T KNOW WHAT HAS HAPPENED WE KNOW TRANSITIONS … BUT WHAT ARE THE INTENTS?

WHAT PART OF THE SYSTEM MADE THE CHANGE?WAS IT A HUMAN OR AN AUTOMATED SYSTEM (WHICH ONE)?

WHAT WAS THE MUTATION? STORING MUTATION AND STATE IS REDUNDANT

WHAT HAPPENS WHEN DELETING AN ENTITY? SHOULD WE DELETE LOGS TOO?

SOLVED

SOLVED

SOLVED

SOLVED

HOW TO ACHIEVE THIS?

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WITH THE HELP OF … CQ(R)S

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COMMAND QUERY SEGREGATION

WRITES READS

ALLOWED TO MUTATE STATE DISALLOWED TO MUTATE STATE

RETURN VOID TYPE RETURN NON-VOID TYPE

COMMANDS QUERIES

! !

WRITE MODELS READ MODELS

CQRS

“IS SIMPLY THE CREATION OF TWO OBJECTS WHERE THERE WAS PREVIOUSLY ONE”

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COMMON ARCHITECTURE

BUS $

HANDLER 1HANDLER 2

…HANDLER N

#

HANDLER 1HANDLER 2

…HANDLER N

COMMAND HANDLERS QUERY HANDLERS

COMMAND = EVENT INPUT = DATA OUTPUT = READ MODEL

M I D D L E W A R E S

WE ARE ALREADY USING “CQRS” YOU KNOW …

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USE CASES

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ALTERNATIVES

SIMPLEBUS/MESSAGEBUS MATTHIAS NOBACK

THEPHPLEAGUE/TACTICIANTHE PHP LEAGUE

QANDIDATE_LABS/BROADWAYQANDIDATE LABS

BEBERLEI/LITECQRS-PHPBENJAMIN EBERLEI

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USAGE

COMMAND HANDLERS QUERY HANDLERS

$bus = $this ->getContainer() ->get('bus');

$cmd = new AcceptOpinion($id, $uId); $bus->handle($command);

$bus = $this ->getContainer() ->get('bus');

$query = new GetLatestOpinions(15); $result = $bus->handle($query);

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CQRS PROS & CONS

PROS CONS

UNIFIED ENTRY POINT

ARCHITECTURE AGNOSTIC

COMPLICATING LOGIC

OUT–OF–BOX SRP

HARDER MAINTENANCE

UNPLANNED MUTATION GIVESUNDESIRED BEHAVIORS

CAN EXTRACT AN API … YAY :)

EASIER TO CACHE READS

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RECOMMENDATION

youtube.com/watch?v=JHGkaShoyNsby GREG YOUNG

QUESTIONS?

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github.com/prgTW

linkedin.com/in/prgTW

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