Software Design Pattern

• Main Principles:-
• KISS (Keep it simple & Stupid)
• SOLID Design Principles
• Regular Expression 
• Twelve-Factor App methodology
• YAGNI (You Ain't Gonna Need It) principle
• Inversion of Control (IoC)
• Law of Demeter: The principle of Least knowledge (only use one dot).
• Composition over inheritance

• Creational Patterns (design patterns that involve instantiating concrete objects.):-
• Factory:-
• a pattern that delegates concrete instantiation to a method of a subclass.
• http://www.itlec.com/2017/05/factory-design-pattern.html
• https://github.com/ITLec/FactoryDesignPattern
• Dependency Injection:-
• Xamarin.Forms
• How Xamarin Handle Multiple Platform In One Code?
• Dependency Injection & Service Locator Example
• Builder.
• Lazy Initialization.
• Prototype:-
• Uses it when creating an instance of a given class is either expensive or complicated.
• Examples:-
• Copy, DeepCopy of an object
• Singletone:-
• Best Implementation For Singleton Design Pattern
• Repository:-
• usually in the midlle between your BAL and DAL, we use it to make it easier in testing.
• Object Pool aka Recycle Bin

• Structural Patterns (design patterns that describe how objects are connected to one another.) :-
• Adapter:-
• a design pattern that connects two incompatible interfaces by fitting between them and providing a compatible interface to both.
• Example
• Bridge (abstraction++):-
• decouple an abstraction from its implementation
• Composite:-
• a design pattern for composing nested structures of objects and dealing with these objects uniformly.
• https://www.dofactory.com/net/composite-design-pattern
• Decorator (Wrapper):-
• the decorator pattern is a design pattern that allows behavior to be added to an individual object, dynamically, without affecting the behavior of other objects from the same class.
• Attaches additional responsibilities to an object dynamically.
• Provide a flexible alternative to sub-classing for extending functionality.
• Example: http://www.itlec.com/2019/06/decorator-design-pattern-example.html
• Facade:-
• a design pattern that involves encapsulating a complex system in a simple interface.
• Flyweight:-
• A space optimization technique that lets us use less memory by storing externally the data associated with similar objects.
• Use it when one instance of a class can be used to provide virtual instances.
• Save memory.
• Front Controller.
• Marker.
• Proxy
• Twin
• Anti-Corruption Layer:-
• Implement a façade or adapter layer between different subsystems that don't share the same semantics.

• Behavioral Patterns (design patterns that focus on how objects distribute work.):-
• Blackboard.
• Chain of responsibility:-
• a behavioural pattern for allowing multiple entities to handle requests.
• Example: http://www.itlec.com/2019/05/chain-of-responsibility-design-pattern.html
• Command:-
• a behavioural pattern for encapsulating requests as objects.
• Example: http://www.itlec.com/2019/06/command-design-pattern.html
• Transaction Command Design Pattern Example.
• Interpreter:-
• Compiler
• Business Rule Engine
• http://www.itlec.com/2019/08/business-rule-engine-linq-expression.html
• Iterator.
• Mediator:-
• a behavioral pattern in which a central object coordinates the activities of many objects.
• For Example: Chat room, Broker 
• Null Object.
• Observer:-
• a behavioural pattern for event handling.
• Publish / Subscribe 
• Servant.
• State:-
• a behavioural pattern for handling requests taking into account the current state of the object.
• Strategy(aka Policy pattern):-
• a class behavior or its algorithm can be changed at run time.
• Instead of using inheritance, you can use behavior interface variable and add setter to those variables.  
• Rule Design Pattern:-
• Most popular example is "Discount example".
• Template Method:-
• a behavioural pattern that allows for similar behaviour to be inherited by multiple subclasses
• How To Implement Template Design Patter Using C#
• Visitor:-
• Use it when you want to add capabilities to a a composite of objects and encapsulation is not important.
• http://www.itlec.com/2021/01/visitor-design-pattern.html
• Memento:-
• provides the ability to restore an object to its previous state.
• Examples:-
• Undo, Restore.
• Provider Pattern :- create pluggable components.
• Context object Design Pattern
• Unit of Work Pattern: usually work with repository pattern to apply set of actions on each CURD operation.

• Concurrency Patterns:-
• Active Object. (Actor, Concurrent Object) - Behavioural patter.
• https://www.dre.vanderbilt.edu/~schmidt/PDF/Act-Obj.pdf
• Balking.
• Block Chain.
• Double-Checked Locking.
• Event-based asynchronous.
• Join
• Lock.
• Monitor Object.
• Reactor.
• Read-Write Lock.
• Scheduler.
• Thread Pool.
• Task-based asynchronous:-
• await/ async

• Architectural patterns:-
• Event Sourcing Pattern
• MVC:-
• stands for Model, View, Controller. A pattern that separates data, display, and control functions into separate roles.
• Is a compound pattern, usually consists of:-
• Observer (model uses observer pattern to keep view/controller/observer updated and decoupled).
• Strategy (Controller is strategy for the view, so the view can use different implementations of the controller to get different behavior).
• Composite (view uses the composite pattern to implement the user interface which usually consists of nested components like panels, frames, buttons…).
• MVVM
• MVP
• VIPER
• N-Tier
• Data Access Object:-
• ORM
• MS Entity Framework:-
• Generic Method To support Update, Insert Delete For Entity Framework C#
• Entity Framework - Exception Handling Method
• Active Record
• Data Transfer Object (DTO):-
• Simple class which contains only the fields with simple getter& setter. without any business inside it.
•  are simple objects that should not contain any business logic but may contain serialization and deserialization mechanisms for transferring data over the wire
• Interceptor
• Service Locator
• Presentation Layer Design Pattern:-
• Intercepting Filter Pattern:-
• Example: Dynamic Filter https://www.c-sharpcorner.com/article/dynamic-filter-by-using-intercepting-filter-pattern/
• Front Controller Design Pattern
• View Helper Pattern
• Composite View Pattern
• Business Layer Design Pattern:-
•  Business Delegate Pattern.
• Service Locator
• Session facade pattern
• Transfer object pattern
• Integration Design Pattern:
• Data access object pattern
• Web Service Broker Pattern

• Data Access Patterns:-
• Repository pattern
• Unit of work
• Lazy load

• Transaction Patterns:-
• Outbox pattern

• SOA Patterns:-
• Canonical model:-
• used to communicate between different data formats.

• Distributed & Scalable Design Patterns/ Algorithms:-
• Enterprise Service Bus ESB
• Microservices Design Patterns:-
• Domain Driven Development
• Aggregator:-
• a service that receives a request, then makes requests of multiple services, combines the results and responds to the initiating request.
• Three ways to implement aggregator:-
• Scatter Gather Pattern
• Chained Pattern:-
• slower pattern than scatter gather pattern.
• Branch Pattern
• Proxy
• Circuit Breaker
• Materialized View Pattern
• Domain Driven Design
• Saga Pattern
• Transactional Outbox Pattern
• 2PC: Two-phase commit protocol:-
• Mainly depends on transaction coordinator, which response for commit/rollback.
• ServiceMesh

• Network Design Patterns:-
• DMZ

• Cloud Design Pattern:-
• Compensating Transaction pattern
• Backends for Frontends pattern
• CQRS (Command Query Single responsibility)

• K8S Multi-Container Design Patterns:-
• Sidecar pattern:-
• eg. file puller
• Ambassador pattern:-
• eg. proxy server.
• Adapter pattern:-
• Transform the application output standardize/ normalized it for aggregation.

TODO:-

https://www.youtube.com/watch?v=LTE6BWfjOUo&list=PLZ9NgFYEMxp4pM7cZTe48udxbI1fR0zbM

https://refactoring.guru/design-patterns

Reference:-

Head First Design Patterns: Building Extensible and Maintainable Object-Oriented Software 2nd Edition

https://en.wikipedia.org/wiki/Software_design_pattern#Creational_patterns

http://www.itlec.com/2016/03/software-design-patterns.html

https://www.javatpoint.com/jee-or-j2ee-design-patterns

https://www.coursera.org/learn/design-patterns

https://patterns.arcitura.com/soa-patterns

https://docs.microsoft.com/en-us/azure/architecture/patterns/

COMP9054: Software Architecture & Design

SOFT8025 - Scalable Microservices

Last update: 20240420