Week 2 Part I · C# and .NET Foundations

Modern C# for Enterprise Domain Models

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

Learning objectives

Use records, nullable reference types, generics, LINQ, exceptions, and async methods idiomatically.
Model entities and value objects from domain language, assuming basic OOP vocabulary is already known.
Separate business invariants from transport and persistence concerns.
Express first domain rules as executable or reviewable examples.

Tools this week

C# 12+domain examplesLINQLINQPad optional

🎓Lecture · 2 hours

0:00-0:10	10 min	Recap and retrieval Review domains and use cases from week 1. Ask what belongs in code before any API exists.
0:10-0:35	25 min	Modern C# type choices Records, init-only properties, required members, readonly members, nullable reference types. Entity identity versus value equality in C# terms.
0:35-1:00	25 min	Generics and reusable policies Generic collections, typed identifiers, result types, and reusable validation policies. Abstractions as contracts at boundaries, not decoration around every class.
1:00-1:10	10 min	LINQ and exceptionsQueries, transformations, and domain-specific failures.
1:10-1:20	10 min	Break
1:20-1:45	25 min	Async and await at boundaries Tasks, non-blocking I/O, cancellation, and common mistakes. Why the domain core should not become async by accident.
1:45-2:00	15 min	From use case to modelTurn a use-case sentence into entities, value objects, and first invariants.

Common misconception to confront.

Students often think: a record is always better because it is shorter.
Set it straight: records are excellent for values and immutable data. Entities with identity and lifecycle need explicit modelling.

Check for understanding

When is a value object a good fit?

When equality is based on the contained values, such as Money, DateRange, Address, or Email.

Why should cancellation tokens appear near I/O boundaries?

They let web requests, database calls, and external calls stop work when the caller no longer needs the result.

Key takeaways.

Modern C# can express domain intent directly.
Good types prevent invalid states.
Clear examples make domain rules reviewable.

📚Reading & resources

C# documentation Official language guide and reference.
LINQ in C# Query syntax and method syntax for collections.
Domain-Driven Design, building blocks chapters Entity, value object, and service vocabulary.

💻Practice · 2 hours

0:00-0:15	15 min	Warm-up kata Implement Money as a value object. Check equality and invalid currency examples.
0:15-0:50	35 min	Domain entities Teams implement first entities for the selected domain. Add constructors or factories that enforce invariants.
0:50-1:10	20 min	LINQ and collections Write query examples over in-memory objects. Discuss what should and should not become a LINQ expression.
1:10-1:20	10 min	Break
1:20-1:50	30 min	Domain-rule examples Write examples for two domain rules. Use assertions that name the business expectation.
1:50-2:00	10 min	Project-integration briefCommit initial domain entities, value objects, and rule examples.

Project integration (this week)

Choose one project domain.
Implement first domain entities and value objects.
Add at least four domain-rule examples.