Domain invariants define the conditions that must remain true throughout a domain object’s lifecycle. Enforcing these conditions within the domain model ensures that object creation and subsequent changes follow business rules without requiring calling code to implement those rules independently.

This session examines how to establish and preserve invariants in C# using principles of domain-driven design. Topics include private constructors and factory methods for controlled creation, guard clauses for validation, private setters and backing fields for encapsulation, read-only collections for protecting aggregate contents, and domain methods for governing state transitions and object mutation. Value objects provide an additional means of enforcing rules for related values.

An Order aggregate serves as the implementation example, demonstrating how these techniques work together and how EF Core persists and materializes the resulting model. Attendees will learn to design domain classes that enforce valid state through their public operations and maintain a clear boundary between business behavior and persistence concerns.

Creating solid invariant domain models prevents code in callers needing to know business rules.