Question

Where should I place the Validation logic of the Domain objects in my solution? Should I put them in the Domain classes, Business layer or else?

I would also like to make use of Validation Application Block and Policy Injection Application Block from Microsoft Enterprise Library for this.

What validation strategy should I be using to fit all these together nicely?

Thanks all in advance!

Answer 1

It depends. First – You need to understand what You are validating.

You might validate:

1. that value You retrieve from Http post can be parsed as date time,
2. that Customer.Name is not larger than 100 symbols,
3. that Customer has enough money to purchase stuff.

As You can see – these validations are different in nature, so they should be separated. Importance of them varies too (see “All rules aren’t created equal” paragraph).

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Thing You might want to consider is not allowing domain object to be in invalid state.

That will greatly reduce complexity because at current time frame, You know that object is valid and You need to validate only current task related things in order to advance.

Also, You should consider avoiding usage of tools in Your domain model because it should be infrastructure free as much as possible.

Another thing – embrace usage of value objects. Those are great for validation encapsulation.