Sample 6 — Validation

Concept: Stratara.Validation — request validation as a mediator pipeline behavior. Invalid commands are rejected at the edge; the handler stays free of guard clauses.

• Code: samples/Stratara.Sample.Validation
• Lines: ~80
• Read time: 5 min
• What it doesn't have: persistence, HTTP — it's a console program focused on the validation pipeline.

What you'll see

1. RegisterUserCommand : ICommand<Guid> and its handler — the handler has no input checks, because validation runs first.
2. RegisterUserValidator : IValidator<RegisterUserCommand> — returns a ValidationResult (never null; ValidationResult.Success when valid). It produces all three severities:
   • Error for a malformed email or under-age request (blocks),
   • Warning for an implausibly high age (passes through, logged).
3. DI wiring via AddStrataraValidation() + AddValidatorsFromAssemblyContaining<Program>(), registered before the handlers so validation is the outermost behavior.
4. StrataraValidationException thrown by the pipeline on Error-severity failures, caught in Program.cs, with its Failures printed.

Running

dotnet run --project samples/Stratara.Sample.Validation

Expected output:

=== Stratara Validation ===

--- Valid command (alice@example.com, age 30) ---
  Handler ran: registered alice@example.com (age 30) as {guid}
  Accepted: {guid}

--- Warning only (bob@example.com, age 150) — passes through, handler still runs ---
warn: ... 1 non-blocking validation failure(s) observed ... request still dispatched to the handler.
  Handler ran: registered bob@example.com (age 150) as {guid}
  Accepted despite the age warning (Warning/Info never block).

--- Invalid command (not-an-email, age 16) — blocked before the handler ---
  Rejected with 2 failure(s):
    [email.invalid] Email: Email must be a non-empty address containing '@'.
    [age.minimum] Age: Age must be at least 18.

Done.

Key takeaways

• Only ValidationSeverity.Error blocks. Warning/Info reach the handler and are logged.
• StrataraValidationException is declared in Stratara.Abstractions.Validation, so a global handler maps Failures to your error model (e.g. RFC-7807 ProblemDetails) without depending on the behavior package.

See the Write a Validator guide for the full walkthrough.