mediatorlite-validation

To add MediatorLite v2 validation without breaking source generation, avoid hand-registering pipeline behaviors and place validators in scanned assemblies so the source-generation-first architecture discovers them automatically. This prevents manual configuration errors while ensuring full validation coverage.

Dual-layer validation in MediatorLite combines built-in Data Annotations attribute checks like [Required] with custom business-rule IValidator<T> implementations. This dual-layer validation model runs attribute checks first, then executes custom validators to enforce complex business rules within the request pipeline.

Duplicate validation behavior execution in MediatorLite is a common v2 anti-pattern caused by manually hand-registering ValidationBehavior<,> instead of relying on source generation. Additionally, throwing exceptions from ValidateAsync instead of returning failure results disrupts the pipeline and causes runtime errors.

To return consistent HTTP 400 error responses for MediatorLite validation failures, implement the error contract using ValidationResult, ValidationError, and ValidationException. This surfaces structured validation errors at API boundaries, ensuring clients receive consistent failure details instead of unhandled exceptions.

Yes, source-generated MediatorLite validation pipelines require .NET 10 or later projects. MediatorLite v2 leverages the source-generation-first architecture available in .NET 10+ to automatically wire validation behaviors, eliminating the need for manual pipeline configuration and preventing duplicate behavior registration.

Use Data Annotations in MediatorLite for basic property-level input validation like [Required] fields, and implement custom IValidator<T> rules for complex business logic such as verifying database record existence. This separation ensures dual-layer validation wiring remains consistent and maintainable.