Re: [netmod] Adding a pre-existing leaf into a new 'choice' - NBC change?

[Andy Bierman <[e-mail]>]

On Thu, Nov 22, 2018 at 5:39 AM Martin Bjorklund <[e-mail]> wrote:

> Hi,
>
> Ladislav Lhotka <[e-mail]> wrote:
> > Andy Bierman <[e-mail]> writes:
> >
> > > On Mon, Nov 19, 2018 at 12:32 PM Sterne, Jason (Nokia - CA/Ottawa) <
> > > [e-mail]> wrote:
> > >
> > >> Hi all,
> > >>
> > >>
> > >>
> > >> If we have a YANG model with a leaf:
> > >>
> > >>
> > >>
> > >> MODEL VERSION 1:
> > >>
> > >> container my-model {
> > >>
> > >>     leaf a { type string; }
> > >>
> > >> }
> > >>
> > >>
> > >>
> > >> And then later we produce another version of the model where that
> leaf is
> > >> placed into a choice construct:
> > >>
> > >>
> > >>
> > >> MODEL VERSION 2:
> > >>
> > >> container my-model {
> > >>
> > >>     choice some-choice {
> > >>
> > >>         case x {
> > >>
> > >>             leaf a { type string; }
> > >>
> > >>         }
> > >>
> > >>     }
> > >>
> > >> }
> > >>
> > >>
> > >>
> > >> Is that considered a non-backwards-compatible change?
> > >>
> > >
> > >
> > > yes -- even though the data node /my-model/x did not change,
> > > the schema node /my-model/a changed to /my-model/some-choice/x/a.
> > > Any leafref path pointing at this leaf will break.
> >
> > This is not correct. A leafref path is a special XPath, and as such
> > includes only data nodes, i.e. NOT choice and case nodes.
> >
> > What does change are schema node identifier. This could be significant
> > in an augment statement, but not ini this example because a leaf cannot
> > be augmented anyway.
> >
> > I don't see anything else that could break, so Jason's change seems
> > backward compatible to me.
>
> Since it does change the schema tree, this is not legal according to
> 7950.  So in that sense it is not backwards compatible.  The rules in
> 7950 protect both clients and other modules that import the module.
>
>
This text is confusing wrt/ schema tree vs data tree:


9.9 <https://tools.ietf.org/html/rfc7950#section-9.9>.  The leafref
Built-In Type

   The leafref built-in type is restricted to the value space of some
   leaf or leaf-list node in the schema tree and optionally further
   restricted by corresponding instance nodes in the data tree.  The
   "path" substatement (Section 9.9.2
<https://tools.ietf.org/html/rfc7950#section-9.9.2>) is used to
identify the referred
   leaf or leaf-list node in the schema tree.  The value space of the
   referring node is the value space of the referred node.





>
> /martin
>
>

Andy


>
>
> >
> > Lada
> >
> > >
> > >
> > > Andy
> > >
> > >
> > >>
> > >> Does the answer depend on whether the choice contains other cases (or
> > >> other cases that are the default case)?
> > >>
> > >>
> > >>
> > >
> > > no
> > >
> > >
> > >> MODEL VERSION 3:
> > >>
> > >> container my-model {
> > >>
> > >>     choice some-choice {
> > >>
> > >>         case x {
> > >>
> > >>             leaf a { type string; }
> > >>
> > >>         }
> > >>
> > >>         case y {
> > >>
> > >>             leaf b { type string; }
> > >>
> > >>         }
> > >>
> > >>     }
> > >>
> > >> }
> > >>
> > >>
> > >>
> > >> A client 'foo' using VERSION 1 would still be able to set & read back
> leaf
> > >> a in the same way as it always did.
> > >>
> > >>
> > >>
> > >> But if another client 'bar' (using VERSION 3) sets leaf 'b', then
> leaf 'a'
> > >> would disappear. That could be surprising to client 'foo' although
> perhaps
> > >> no more surprising than if another client simply deletes leaf 'a'
> (using
> > >> VERSION 1).
> > >>
> > >>
> > >>
> > >> Jason
> > >>
> > >>
> > >>
> > >>
> > >>
> > >>
> > >> _______________________________________________
> > >> netmod mailing list
> > >> [e-mail]
> > >> https://www.ietf.org/mailman/listinfo/netmod
> > >>
> > > _______________________________________________
> > > netmod mailing list
> > > [e-mail]
> > > https://www.ietf.org/mailman/listinfo/netmod
> >
> > --
> > Ladislav Lhotka
> > Head, CZ.NIC Labs
> > PGP Key ID: 0xB8F92B08A9F76C67
> >
> > _______________________________________________
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> >
>