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

Martin Bjorklund <mbj@tail-f.com> Mon, 19 November 2018 20:46 UTC

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Date: Mon, 19 Nov 2018 21:46:22 +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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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
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