Should Business Objects or Entities be Self-Validated?

Question

Validation of Business Objects is a common issue, but there are some solutions to solve that.

One of these solutions is to use the standalone NHibernate.Validator framework, which is an attribute-based validation framework.

But I'm facing into conceptual concern. Attribute validators like NH.Validator are great but the validation is only performed when save-update-delete within the Session.

So I wonder if business objects should not be self-validated in order to maintain their own integrity and consistence?

Answer 1

IMHO - there are 2 steps of validations needed for a Business Object (BO)/Entity to be valid:

Step1: BO/Entity self-validation - In this, we check only if the entity is valid in terms of its state F.Ex.: If postal code is set, then does it have valid characters & is of valid length etc. form the BO/Entity level validations. But beyond this level of validation, we would not be able to say that the BO/Entity is valid in your business domain and/or repository. Typically the BO/Entity would be able to enforce this level of validation.

Step2: Context validation - In this, we need to validate if the BO/Entity is valid within the context of the Repository where it is being persisted. F.Ex.: Is the postal code valid for the country in which the order is being placed/sent to etc. For this validation, some or all entities in the current context might need to be involved to make sure the BO/Entity is valid.

So, to keep the entities pure, you will need to split the validation into these 2 steps - one performed by the entity itself & the second by the repository which is persiting/working with the entity.

HTH.