[bv-dev] Node#getElementDescriptor() for user-created nodes

[Emmanuel Bernard]

BTW a softer solution is to make the behavior non portable. ie it could
be an exception, or there could be some proprietary virtual nodes.
That's not very satisfactory though and is likely going to block up in
the future.

On Fri 2013-02-08 19:11, Emmanuel Bernard wrote:
> I had the same reserve as you but then reading the JavaDoc made me
> realize that the doc mentions properties so it is technically not as
> vague as I initially thought.
> 
> Emmanuel
> 
> On Fri 2013-02-08 11:48, Matt Benson wrote:
> > Personally my reason for eschewing option #1 is the possibility of breaking
> > existing code.
> > 
> > Matt
> > 
> > 
> > On Fri, Feb 8, 2013 at 11:22 AM, Emmanuel Bernard <emmanuel at hibernate.org>wrote:
> > 
> > > At this time of day I do tend to like option #1 (ie making virtual nodes
> > > illegal). Otherwise my preferred option is #4
> > > (VirtualElementDescriptor).
> > >
> > > Out of curiosity for people not preferring option #1. What use case do
> > > you see in having virtual nodes?
> > >
> > > Emmanuel
> > >
> > > On Fri 2013-02-08 11:08, Matt Benson wrote:
> > > > Hmm, a third option for the elementClass of such a descriptor might be
> > > > Void.class.
> > > >
> > > > I prefer option #3, followed by #4.
> > > >
> > > > Matt
> > > >
> > > >
> > > > On Fri, Feb 8, 2013 at 5:17 AM, Gunnar Morling <gunnar at hibernate.org>
> > > wrote:
> > > >
> > > > > Hi experts,
> > > > >
> > > > > One of the remaining issues on our way to 1.1 is BVAL-336 [1], which is
> > > > > about what to return from Node#getElementDescriptor() for nodes added
> > > by
> > > > > the user via the ConstraintViolationBuilder API.
> > > > >
> > > > > Note that as per the spec only sub paths can be created by the user,
> > > i.e.
> > > > > user added nodes always represent properties but e.g. no methods or
> > > > > parameters. Based on that, it seems right to return the correct
> > > > > PropertyDescriptor in case a user adds a node for an existing property.
> > > > >
> > > > > Things get tricky though when nodes are added for non-existent
> > > properties.
> > > > > Emmanuel, Hardy and I identified the following options to address this
> > > > > situation:
> > > > >
> > > > > #1 Disallow adding non-existent nodes
> > > > >
> > > > > In case a user adds a node but no property with that names exist, an
> > > > > exception is thrown. The problem is elegantly avoided that way, but we
> > > > > might break some 1.0 user code (currently the spec is not really clear
> > > > > whether added nodes must exist or not).
> > > > >
> > > > > #2 return null from getElementDescriptor()
> > > > >
> > > > > When invoking getElementDescriptor() on a Node representing a
> > > non-existent
> > > > > property, null could be returned. This seems consistent (there is no
> > > > > element), but causes additional null checking when traversing a path.
> > > > >
> > > > > #3 return a PropertyDescriptor from getElementDescriptor()
> > > > >
> > > > > Since all user-added nodes represent properties, a PropertyDescriptor
> > > > > could be returned. hasConstraints() would return false,
> > > > > getConstraintDescriptors() the empty set etc. This would allow to
> > > handle
> > > > > all nodes and their descriptors uniformly when traversing a path.
> > > Question
> > > > > is what to return from PropertyDescriptor#getElementClass(). Options
> > > are to
> > > > > return null (signaling that the property is non-existent) or
> > > Object.class.
> > > > >
> > > > > #4 return a VirtualDescriptor from getElementDescriptor()
> > > > >
> > > > > We could create a new Kind, VIRTUAL, and an accompanying type
> > > > > VirtualDescriptor and return an instance of this. Behavior of the
> > > methods
> > > > > on the descriptor would be basically the same as in #3; getKind()
> > > returning
> > > > > Kind.VIRTUAL would allow for a very explicit checking whether the node
> > > > > exists or not.
> > > > >
> > > > > Any feedback on the options (ideally with arguments pro/con) or other
> > > > > alternatives are highly welcome. As life goes, Emmanuel's, Hardy's and
> > > my
> > > > > preferences are equally distributed between these options :)
> > > > >
> > > > > Thanks,
> > > > >
> > > > > --Gunnar
> > > > >
> > > > > [1] https://hibernate.onjira.com/browse/BVAL-336
> > > > >
> > > > >
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> > > > >
> > >
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