CQRS … AND EVENT SOURCING 03
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CQRS
… AND EVENT SOURCING
03
CQRS EVENT SOURCING
… AND CQRS … AND EVENT SOURCING
03
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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