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

Martin Bjorklund <mbj@tail-f.com> Tue, 20 November 2018 07:34 UTC

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Date: Tue, 20 Nov 2018 08:33:59 +0100 (CET)
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To: jason.sterne@nokia.com
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From: Martin Bjorklund <mbj@tail-f.com>
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Subject: Re: [netmod] Adding a pre-existing leaf into a new 'choice' - NBC change?
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Martin Bjorklund <mbj@tail-f.com> wrote:
> Hi,
> 
> "Sterne, Jason (Nokia - CA/Ottawa)" <jason.sterne@nokia.com> 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
  ^^^^^^^^^^^^^^^^^

I meant, "Yes, accordning to current RFC 7950 rules this is not
allowed".   But I think you got that.


/martin

> 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
> 
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