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DESIGN PATTERNS IN PHP APPLICATIONS INVIQA ENLIGHTENING LUNCH ARTURAS “2 SHEDS” SMORGUN

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IN SOFTWARE ENGINEERING DESIGN PATTERN IS ! ! !

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IN SOFTWARE ENGINEERING DESIGN PATTERN IS A REUSABLE SOLUTION ! !

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IN SOFTWARE ENGINEERING DESIGN PATTERN IS A REUSABLE SOLUTION TO COMMON PROBLEM !

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IN SOFTWARE ENGINEERING DESIGN PATTERN IS A REUSABLE SOLUTION TO COMMON PROBLEM WITHIN A GIVEN CONTEXT

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MOTIVATION? REINVENTION OF SOLUTIONS; COMMUNICATION PROBLEMS.

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CONCERNS? EASY TO OVER USE; WILL LEAD TO MORE MESS IF CHOSEN WRONG PATTERN.

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DESIGN PATTERNS ELEMENTS OF REUSABLE OBJECT ORIENTED SOFTWARE

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! GANG OF FOUR ERICH GAMMA, RICHARD HELM, RALPH JOHNSON, JOHN VLISSIDES.

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23 CLASSIC DESIGN PATTERNS

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CREATIONAL PATTERNS FACTORY METHOD, SINGLETON, ABSTRACT FACTORY, BUILDER, PROTOTYPE.

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STRUCTURAL PATTERNS ADAPTER, BRIDGE, COMPOSITE, DECORATOR, FACADE, FLYWEIGHT, PROXY.

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BEHAVIOURAL PATTERNS CHAIN OF RESPONSIBILITY, COMMAND, INTERPRETER, ITERATOR, MEDIATOR, MEMENTO, OBSERVER, STATE, STRATEGY, TEMPLATE METHOD, VISITOR.

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“EXTRAS” CONCURRENCY PATTERNS, ARCHITECTURAL PATTERNS, MANY MORE…

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“GANG OF FOUR” FOR AVERAGE BEGINNER PHP DEVELOPER (ME, NOT LONG WHILE AGO)

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FACTORY METHOD, SINGLETON, OBSERVER, ITERATOR.

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POPULAR IN PHP DEPENDENCY INJECTION (STRUCTURAL), FRONT CONTROLLER (ARCHITECTURAL), MODEL VIEW CONTROLLER (ARCHITECTURAL), FACTORY (CREATIONAL), SINGLETON (CREATIONAL), OBSERVER (BEHAVIOURAL).

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REVIEW OF PATTERNS
 IN PHP SOFTWARE. BRIEF, OPINIONATED, NOT PRECISE.

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WHAT’S HOT? MODEL VIEW CONTROLLER, FRONT CONTROLLER, FACTORY METHOD, OBSERVER, REGISTRY, DECORATOR, VISITOR, …

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MVC ARCHITECTURAL PATTERN. THREE TIER ARCHITECTURE TO RELATE USER INTERFACE TO UNDERLYING DATA MODELS.

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TYPICAL MVC DIAGRAM

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MODEL DATA AND BUSINESS LOGIC.

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VIEW INTERFACE TO VIEW AND MODIFY DATA

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CONTROLLER THIN MID LAYER BETWEEN MODEL AND VIEW: 1. ACCEPTS INPUT 2. EXECUTES COMMANDS ON MODEL 3. GENERATES OUTPUT

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IMPLEMENTATION IN MAGENTO

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IMPROVEMENTS? 1. MORE SEPARATED TIERS. 2. “THINNER” CONTROLLERS. 3. “DUMB” VIEWS.

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FRONT CONTROLLER ARCHITECTURAL PATTERN. PROVIDES CENTRALISED ENTRY POINT FOR HANDLING REQUESTS. SPECIALISED CASE OF MEDIATOR PATTERN.

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MEDIATOR PATTERN BEHAVIOURAL PATTERN. DEFINES AN OBJECT, WHICH DECIDES HOW A SET OF OBJECTS INTERACTS.

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TYPICAL MEDIATOR DIAGRAM

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MEDIATOR DEFINES AN INTERFACE FOR COMMUNICATING WITH COLLEAGUE OBJECTS.

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CONCRETE MEDIATOR IMPLEMENT COOPERATIVE BEHAVIOUR; KNOWS AND MAINTAINS IT’S COLLEAGUES.

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C0LLEAGUE KNOWS IT’S MEDIATOR; COMMUNICATES WITH MEDIATOR INSTEAD OF OTHER COLLEAGUES.

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IMPLEMENTATION IN OXID

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SINGLETON CREATIONAL (ANTI)PATTERN. ENSURES A CLASS HAS ONLY ONE INSTANCE. PROVIDES A GLOBAL POINT OF ACCESS TO IT. AVOID AT ANY COST!

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WHERE IT’S USED? MAGENTO, SILVERSTRIPE, PRESTASHOP, OXID.

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WHY IT’S SO BAD? GLOBAL INSTANCE - HIDING DEPENDENCIES; USUALLY LEADS TO TIGHT COUPLING; USUALLY CARRIES AROUND GLOBAL STATE; STATIC CALL - HARD TO MOCK.

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ALTERNATIVES? USE A FACTORY INSTEAD; INSTANTIATE AT THE TOP OF APP PASS TO COMPONENTS VIA DEPENDENCY INJECTION.

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REGISTRY STRUCTURAL PATTERN (NOT GOF). A CONTAINER OF SHARED OBJECTS.

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DANGEROUS? OFTEN USED WITH STATIC CALLS. WHEN ABUSED LEADS TO HIDDEN DEPENDENCIES.

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EXAMPLE FROM OPENCART

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EXAMPLE FROM SYLIUS

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HOW TO IMPROVE? BEING DISCIPLINED ABOUT WHAT TO STORE IN REGISTRY, NOT USING STATIC CALLS.

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DECORATOR STRUCTURAL PATTERN. ATTACH ADDITIONAL RESPONSIBILITIES TO AN OBJECT DYNAMICALLY.

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TYPICAL DECORATOR DIAGRAM

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COMPONENT DEFINES AN INTERFACE FOR OBJECT THAT CAN HAVE RESPONSIBILITIES ADDED TO THEM DYNAMICALLY.

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CONCRETE COMPONENT DEFINES AN OBJECT TO WHICH ADDITIONAL RESPONSIBILITIES CAN BE ATTACHED.

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DECORATOR MAINTAINS A REFERENCE TO A COMPONENT OBJECT; DEFINES AN INTERFACE THAT CONFORMS TO COMPONENT’S INTERFACE.

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CONCRETE DECORATOR ADDS RESPONSIBILITIES TO THE COMPONENT.

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EXAMPLE FROM SILVERSTRIPE

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ALTERNATIVE? STRATEGY DESIGN PATTERN

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STRATEGY BEHAVIOURAL PATTERN. DEFINES A FAMILY OF ALGORITHMS AND MAKE THEM INTERCHANGEABLE.

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TYPICAL STRATEGY DIAGRAM

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STRATEGY DECLARES AN INTERFACE COMMON TO ALL SUPPORTED ALGORITHMS; IS USED BY CONTEXT TO CALL ALGORITHM.

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CONCRETE STRATEGY IMPLEMENTS THE ALGORITHM USING STRATEGY INTERFACE.

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CONTEXT IS CONFIGURED WITH A CONCRETE STRATEGY OBJECT; MAINTAINS A REFERENCE TO A STRATEGY OBJECT; DEFINES INTERFACE FOR STRATEGY TO ACCESS ITS DATA (OPTIONAL).

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DIFFERENCES FROM DECORATOR SWITCHES ENTIRE ALGORITHM RATHER THAN WRAPS IT UP.

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COMMON ANTIPATTERNS STATIC CALLS, EXCESSIVE USE OF GLOBAL CONSTANTS, EXCESSIVE USE OF MAGIC, SINGLETONS, GOD CLASSES.

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WHAT’S MY POINT?

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DESIGN PATTERNS ARE NOT THAT WIDE SPREAD. MANY FRAMEWORKS MAKE USE OF LIMITED SUBSET OF THEM. THERE ARE ALSO N WAYS TO IMPLEMENT DESIGN PATTERN.

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THERE IS ALTERNATIVE TO EVERYTHING. BE AWARE OF YOUR OPTIONS AND KNOW WHERE TO LOOK IT UP WHEN NEEDED.

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KNOWING ANTIPATTERNS IS IMPORTANT TO RAISE AWARENESS AND NOT TO FALL INTO THE SAME TRAP AS PROCEEDERS DID.

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INSTEAD OF QUESTIONS: GO AND DISCUSS WITHIN YOUR TEAM.

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THANK YOU.