Week 7 Part III · Architecture and Patterns

Enterprise Design Patterns I

Instructor lesson plan: lecture (2 h) and practice (2 h).

Learning objectives

Apply Repository, Unit of Work, Factory, Strategy, Adapter, and Decorator in realistic .NET systems.
Choose patterns because they clarify boundaries or variation points.
Explain pattern tradeoffs in project documentation.

Tools this week

DI containerinterfacespattern notesdesign notes

🎓Lecture · 2 hours

0:00-0:15	15 min	Pattern vocabularyPattern as named tradeoff, not copied ceremony.
0:15-0:40	25 min	Repository and Unit of WorkPersistence boundary, query needs, EF Core realities, and when direct DbContext is acceptable.
0:40-1:05	25 min	Factory and StrategyCreation rules and policy variation in business workflows.
1:05-1:15	10 min	Break
1:15-1:40	25 min	Adapter and DecoratorExternal services, logging, caching, validation, and cross-cutting behavior.
1:40-2:00	20 min	Pattern selection rubricWhat problem exists, what changes independently, and what cost the pattern adds.

Common misconception to confront.

Students often think: more patterns means better architecture.
Set it straight: patterns are useful only when they remove real coupling or name real variation.

Check for understanding

When is Strategy useful?

When a family of algorithms or policies varies independently from the workflow that uses it.

What is Adapter protecting?

The application from the shape, instability, or vendor-specific contract of an external dependency.

Key takeaways.

Patterns name design choices.
Each pattern must earn its place.
Documentation should explain the problem solved.

📚Reading & resources

Design Patterns Factory, Strategy, Adapter, and Decorator chapters.
DDD and CQRS patterns in .NET Microsoft architecture guidance.

💻Practice · 2 hours

0:00-0:25	25 min	Pattern diagnosisStudents inspect project code and identify two real variation points.
0:25-1:00	35 min	Implement one patternAdd Strategy, Adapter, Factory, or Decorator with a clear usage example.
1:00-1:10	10 min	Break
1:10-1:45	35 min	Implement second patternAdd a second pattern and verify it does not leak into controllers.
1:45-2:00	15 min	Project-integration briefDocument each pattern: problem, solution, tradeoff, example.

Project integration (this week)

Implement at least two enterprise design patterns.
Add examples showing the behavior they protect.
Write a short design note for each pattern.