[hibernate-dev] [Validator] Applying constraints to property objects

[Emmanuel Bernard]

On Wed 2013-09-04  9:26, Gunnar Morling wrote:
> 2013/9/4 Emmanuel Bernard <emmanuel at hibernate.org>
> 
> > On Wed 2013-09-04  8:27, Gunnar Morling wrote:
> > > 2013/9/3 Emmanuel Bernard <emmanuel at hibernate.org>
> > >
> > > > Something like c makes sense.
> > > >
> > >
> > > Ok.
> > >
> > >
> > > > It similar to the notion of converter in JPA.
> > > >
> > > > But why not the following style of interfaces
> > > >
> > > >     interface Convert<From,To> {
> > > >         To convert(From);
> > > >     }
> > > >
> > >
> > > Yes, thinking more about it, it probably makes sense to support multiple
> > > converters, e.g. in case someone works with UIInput and *Property in the
> > > same application. Then the "From" parameter makes sense to avoid casts
> > > within the converter implementation. Need to experiment with it a bit.
> >
> > More than just the cast in the impl, its a way to statically know that
> > you have a converter that takes From and only From, so you can restrict
> > the list of converters to consider to 0 or 1 all the time (assuming we
> > don't support multiple converters of the same From.
> >
> > >
> > > Regarding the name, I find "Converter" a bit too generic, in particular
> > > since it needs not only to convert the actual property value but also the
> > > static type so you can reject this (because @Size can't be applied to
> > > Object):
> >
> > Not sure I follow, before the core HV work, it converts a property or
> > class from From to To and from there you are good to go.
> >
> > Are you saying that if From = UIInput<String> we would not be able to
> > separate it from UIInput<Object> statically? I *think* we can, just like
> > we do for collections in JPA.
> >
> 
> No, I'm not saying that. I also think we can separate that.
> 
> There is two steps involved:
> 
> * Resolve the correct validator for the validated element, using its
> declared (static) type; E.g. in the following case we'd need to find the
> validator for @Size/String:
> 
>     @Size(min=3)
>     UIInput<String> name;
> 
> While in this case we'd have to throw an exception since there is no
> validator for @Size/Object:
> 
>     @Size(min=3)
>     UIInput<Object> name;
> 
> For this step I envisioned the method "Type getDeclaredType(Type
> sourceType)" (better name to be found, unwrapDeclaredType()?), which would
> return the "real" type to consider for validator resolution (here, String
> or Object, respectively).
> 
> * If we have found the right validator, use it to validate the given value.
> For this step I envisioned the getValidatedValue() method which obtains the
> value from the given wrapped property before passing it to the validator.

What I am arguing then is that the getDeclaredType method is unnecessary if
the converter class captures the type already via the From parameterized
type.