Design Patterns Using .NET — Lesson 3: Behavioral and Domain Patterns

Learning Objectives

• Use strategy, command, observer, state, template method, mediator, and chain of responsibility
• Apply repository, unit of work, specification, and domain-service concepts
• Model changing behavior, workflows, events, and business rules

Detailed Topics

• Use strategy: Use strategy, command, observer, state, template method, mediator, and chain of responsibility
• Apply repository: Apply repository, unit of work, specification, and domain-service concepts
• Model changing behavior: Model changing behavior, workflows, events, and business rules

Guided Demonstration

1. Review the requirement, users, data, dependencies, permissions, risks, and expected result.
2. Demonstrate the relevant configuration, development, administration, analysis, or collaboration workflow step by step.
3. Capture settings, outputs, logs, screenshots, calculations, test results, and other useful evidence.
4. Compare the observed result with acceptance criteria and explain any corrective action.

Hands-On Activity

Implement a flexible business workflow using behavioral patterns.

• Document assumptions, prerequisites, and the planned sequence before starting.
• Complete the activity and preserve evidence of normal, boundary, and failure behavior.
• Record issues, corrective actions, reusable notes, and the next improvement priority.

Scenario Analysis

• Identify the business or technical decision that must be made.
• Compare valid implementation approaches and their trade-offs.
• Consider security, privacy, accessibility, performance, support, and operational impact.

Troubleshooting Focus

• Separate symptoms from causes and collect evidence before applying a fix.
• Check configuration, data, permissions, dependencies, capacity, connectivity, and recent changes.
• Validate rollback, recovery, ownership, user impact, and business continuity.

Validation Checklist

• The requirement, scope, inputs, and expected outcome are clear.
• The selected design or configuration is documented and follows approved standards.
• Normal, boundary, failure, security, accessibility, and operational conditions are reviewed.
• The result is supported by evidence and the next improvement is prioritized.

Lesson Outcome

Learners can explain and apply Behavioral and Domain Patterns in a realistic scenario and validate the result with documented evidence.