Re: [netmod] choice statements and trim vs explicit default handling

[Robert Wilton <[e-mail]>]

Hi Jason,

Your default statement in your YANG snippet below would be ignored, as 
per section 7.9.3 of RFC 7950.

But, if you changed your YANG to this:

choice foo {

   default aa;

   case aa {

     leaf some-bool { type Boolean; default “false”; }

   {

   case bb {

     leaf some-num { type int32; }

   }

}


Then answering both (A) and (B): I would assume that setting "some-bool" 
to "true" or "false" would cause "bb" to be deleted regardless of what 
default mode the server was using.  If neither some-bool or some-num had 
been set to an explicit value then some-bool semantically exists with 
value "false" due to the two default statements.

I might be wrong, but I have always assumed that the with-defaults 
extension is really concerned with the presentation/encoding of default 
values, and isn't intended to change the underlying semantics of YANG's 
handling of default values.

Thanks,
Rob


On 07/04/2017 23:50, Sterne, Jason (Nokia - CA/Ottawa) wrote:
>
> Hi all,
>
> When a server operates in ‘trim’ mode (rfc6243), setting a leaf to its 
> default value removes it from the config (i.e. it is indistinguishable 
> from the case where that leaf was never configured or the case where 
> that leaf was deleted/removed).
>
> (A)
>
> Does setting a leaf in one case of a choice to its default value (in a 
> ‘trim’ mode server) cause leafs in other cases to be implicitly 
> deleted ?  I assume not.
>
> For example:
>
> choice foo {
>
>   case aa {
>
>     leaf some-bool { type Boolean; default “false”; }
>
>   {
>
>   case bb {
>
>     leaf some-num { type int32; }
>
>   }
>
> }
>
> If some-num is currently set to 50, and then an edit-config sets 
> some-bool to “false”, does that clear the some-num leaf ?
>
> (i.e. does it select case aa ?)
>
> RFC 7950 says: “the creation of a node from one case implicitly 
> deletes all nodes from all other cases”.
>
> RFC 6243 section 2.2.3 describes that a leaf set to default (in a trim 
> server) doesn’t exist.
>
> (B)
>
> Now how about if the server operates in ‘explicit’ mode ?  Does 
> setting some-bool to “false” clear some-num ?  I assume it does (but 
> it just seems a little funny that the behavior on this changes between 
> trim and explicit servers).
>
> Regards,
>
> Jason
>
>
>
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