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

["Sterne, Jason (Nokia - CA/Ottawa)" <[e-mail]>]

Thanks. I forgot that the choice is in the *schema* path (was thinking about the instance data path which doesn't include the choice or case statements).

> -----Original Message-----
> From: Martin Bjorklund <[e-mail]>
> Sent: Monday, November 19, 2018 3:46 PM
> To: Sterne, Jason (Nokia - CA/Ottawa) <[e-mail]>
> Cc: [e-mail]
> Subject: Re: [netmod] Adding a pre-existing leaf into a new 'choice' - NBC
> change?
> 
> Hi,
> 
> "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?
> 
> Not accordning to current RFC 7950 rules, since it changes the schema
> node path (suppose the leaf was a container, and someone had augment
> /my-model/a).
> 
> > 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).
> 
> 
> 
> /martin