Richard Wallace wrote:
> Is that the way that it is intended to work? I thought I read
> somewhere, though I can't find it now, that the constraints would be
> checked at the end of the unit of work. I thought this would be a nice
> way to allow my validation to happen in the domain layer and propagate
> the violation messages to the application for them to be displayed to
> the user.
Right, the idea was initially to allow it to happen "late", but it just
became a wee bit too complex.
> The way it is currently implemented only the first constraint violation
> would be reported to the user, making it unusable as a general way of
> doing validation as it would require the user to submit the form, fix
> the first validation error, submit the form, fix the next validation
> error, ad nauseum as opposed to having all the constraint violations
> checked at the end of the unit of work and reporting all violations at
> once.
My current thinking is that when a form is submitted all properties will
be set *regardless of whether any of them causes constraint errors*.
I.e. set a property and if it causes an exception then simply continue
to the next and do that too, and in the end if there were 1 or more
execptions, present these to the user. That should solve it I think, but
it requires the UI layer to be aware of this semantics, which I think is
fine.
> The other problem with this mechanism is that it requires a setter to be
> called for any validation to be performed. The problem with this is
> that it could allow invalid data to pass. For instance, in the Nameable
> example that I've used elsewhere we have
>
> public interface Nameable {
> @NonEmptyString Property<String> name();
> }
>
> That non-empty string constraint is only ever going to be checked when
> nameable.name().set(something) is called. If someone where to simply
> create the entity and never call that setter, we'd wind up with an
> invalid object in our entity store.
I have now implemented support for UnitOfWorkSynchronization callbacks
which allow you to register validation rules that are called before
complete() is done. Things like the above should be checked during this
phase, which will solve it I hope. Try it out and see how it goes.
/Rickard
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