Defining a new constraint without a new annotation

javierpaniza · **Posted:** Fri Apr 11, 2008 1:15 pm

It's very frecuent in business application to write not reusable validations. In this case, if we force the developer to write an annotation for each validation, in addition to the java code for the validation; we are adding bureaucratic work for the developer.

My suggestion is to include a built in constraint in JSR-303 called @Constraint, @Validator, @GenericConstraint or so, that can be used in this way:

Code:

@Validator(InvoiceConstraint.class)
public class Invoice {
   ...
}

Where InvoiceConstraint implements Constraint.

Because the validation logic for Invoice can be used only on Invoice, we do not need to define an annotation for it, only the class, therefore you will save a lot of bureaucratic code.
This is in the spirit of the @ProperyValidator
http://openxava.wikispaces.com/model_en#toc11
and @EntityValidator
http://openxava.wikispaces.com/model_en#toc19
annotations of OpenXava

What do you think ?

bodrin · **Joined:** Thu Apr 17, 2008 5:47 pm **Posts:** 26

Very good idea!

For example I have a domain model and a set of message classes (send/recv via JMS) and each message class contains an instance of the domain model part - a subgraph.
Every such message class should validate first that the subgraph structure it carries is valid, then it should validate each instance there.
So the validation of each message class (the subgraph structure) is applicable only for it and not usable anywhere else.

emmanuel · **Posted:** Wed Apr 23, 2008 8:20 pm

I don't see it as bureaucratic as it adds readability to the code base.

But nothing prevents you from writing such a generic annotation.

javierpaniza · **Posted:** Thu Apr 24, 2008 2:03 pm

emmanuel wrote:

I don't see it as bureaucratic as it adds readability to the code base.

Writting more code for obtain the same result is not good. At least I don't like. Maybe I have write a lot of EJB code in my life. And now I'm very sensible to bureaucratic code.
I'm sure that if you would write an application with a different validation for each model class, with more than 50 model classes, at the end you will write for yourself this annotation.

emmanuel wrote:

But nothing prevents you from writing such a generic annotation.

It's already written, and it is a Hibernate Validator constraint, you can see it here:
http://www.gestion400.com/OpenXavaDoc/a ... dator.html

But, it's important to include it (or one alike) in JSR-303. When more build in annotations more portability of the model classes between frameworks.

Cheers

emmanuel · **Posted:** Thu Apr 24, 2008 3:15 pm

I ahve noted the point. Let's see how the EG like the idea