Software Engineering Fundamentals (SEF): MS.NET Design Patterns

Origin and history
Book about architectural patterns by Christopher Alexander (1977)
Kent Beck’s and Ward Cunningham’s presentation at OOPSLA (1987)
Book about software design patterns by gang of four (1994)
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

What they are?
Reusable templates for solving recurring software design problems.
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Why they matter?
No need to discover (productivity)
Solution verified over time (reliability)
Common language for developers
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Use and misuse
Apply design patterns only when needed and only those which give benefit in your context.
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Classification
Creational (Builder, Singleton, Factory, …)
Structural (Facade, Decorator, Composite, …)
Behavioral (Strategy, Chain of responsibility, …)
…
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Simple factory
Class which defines a method for creating instances of other classes.
Not actually a pattern.
Advantages?
Construction logic is separated
Dependent object can be easier switched (unit testing, …)
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Facade
Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.
Advantages?
Client code is decoupled from subsystem
Interaction with subsystem in single place
Simplified interface to set of classes
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Repository
Mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects.
Advantages?
Centralized data access
Business logic is decoupled from data access
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Decorator
Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
Advantages?
Helps avoid class explosion
Behavior can be added\changed dynamically
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Template method
Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.
Advantages?
Facilitates code reuse
Algorithm structure in single place
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Summary
Avoid POTY (Pattern Of The Year) syndrome
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

References
GoF design patterns (dofactory)
Pattern classification (gofpatterns)
Head First Design Patterns book
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Video Tutorials
Factory - https://www.youtube.com/watch?v=ub0DXaeV6hA
Facade - https://www.youtube.com/watch?v=B1Y8fcYrz5o
repository - https://www.youtube.com/watch?v=rtXpYpZdOzM
decorator - https://www.youtube.com/watch?v=j40kRwSm4VE
template - https://www.youtube.com/watch?v=aR1B8MlwbRI
Full PlayList with aditional patterns :
https://www.youtube.com/watch?v=vNHpsC5ng_E&list=PLF206E906175C7E07
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.

Code examples
https://github.com/maksims-ahadovs/Design-Patterns
© Accenture. By Maksims Ahadovs, Dmitri Kartashov-Gawski & Artem Slobolinskyi.