Re: [netmod] YANG 'must' Xpaths, predicates and wildcards

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

Thx.  In the case I'm most concerned about, a-list (and all descendants) is config true and 'entry' is the key leaf.  So all a-list entries have a node called 'entry' by definition.

(I'm regretting using the name 'entry' for my key now in this example 😊

In this case it seems all the following result in the equivalent behavior (checking that a-list has at least one entry):
	must "../a-list";
	must "../a-list[entry=*]";
	must "../a-list[entry]";  <- this confuses me but I'll take your word for it
	must "../a-list/entry";
	must "../a-list[entry=*]/entry";
	must "../a-list[entry]/entry";  <- not sure about this one

Rgds,
Jason

> -----Original Message-----
> From: Martin Bjorklund [mailto:[e-mail]]
> Sent: Wednesday, March 28, 2018 1:28 PM
> To: Sterne, Jason (Nokia - CA/Ottawa) <[e-mail]>
> Cc: [e-mail]; [e-mail]
> Subject: Re: [netmod] YANG 'must' Xpaths, predicates and wildcards
> 
> "Sterne, Jason (Nokia - CA/Ottawa)" <[e-mail]> wrote:
> > Thanks Alex.  Sorry about those sloppy mistakes.  I agree about the
> > ../a-list and I should have said count > 0.
> >
> > In the 2nd part of my email, my intention was to only allow foo to be
> > configured if a-list has at least one entry configured.  So I don't
> > think min-elements 1 would work.  I don't want to always require an
> > entry in a-list.  I only want to require one if foo is configured.
> >
> > I guess this also achieves the same thing right ?
> >       must "../a-list[entry=*]";
> 
> Yes, if all a-list entries has a node called "entry".  But if that't
> what you want, do:
> 
>        must "../a-list[entry]";
> 
> 
> > If foo has a default value, then does that mean the "must" is
> > evaluated even if foo is deleted from the config ?
> >     leaf foo {
> >       must "../a-list";   <- always evaluated because of default ?
> >       type uint16;
> >       default 5;
> >     }
> > If the must is always evaluated then it would be the equivalent of
> > having min-elements 1 in a-list.
> 
> 
> Correct.
> 
> 
> /martin
> 
> >
> > Rgds,
> > Jason
> >
> > From: Alex Campbell [mailto:[e-mail]]
> > Sent: Tuesday, March 27, 2018 9:57 PM
> > To: Sterne, Jason (Nokia - CA/Ottawa) <[e-mail]>;
> > netmod@ietf..org
> > Subject: Re: YANG 'must' Xpaths, predicates and wildcards
> >
> >
> > Hi,
> >
> >
> >
> > For one thing, it should be ../a-list since a-list is not a child of
> > foo.
> >
> > Also - if foo is not configured and has no default value, then any
> > must expressions in foo are not evaluated because it is not part of
> > the "accessible tree". (I tested this in ConfD)
> >
> > Apart from these issues, yes it will behave as you expect - it will
> > fail if a-list contains no entries.
> >
> >
> >
> > must "count(a-list) > 1"; is not equivalent since it requires at least
> > two entries.
> >
> >
> >
> > However, you can more simply add a min-elements 1; statement to a-list
> > to achieve the same goal - no XPath required.
> >
> >
> >
> > ________________________________
> > From: netmod <[e-mail]<mailto:netmod-
> [e-mail]>>
> > on behalf of Sterne, Jason (Nokia - CA/Ottawa)
> > <[e-mail]<mailto:[e-mail]>>
> > Sent: Wednesday, 28 March 2018 1:10 p.m.
> > To: [e-mail]<mailto:[e-mail]>
> > Subject: [netmod] YANG 'must' Xpaths, predicates and wildcards
> >
> > Hi all,
> >
> > I'm pretty sure that this xpath (e.g. in a must statement) isn't
> > correct:
> >
> >               (A) ../container-a/list-b[name=*]/some-leaf
> >
> > and should just be this instead:
> >
> >               (B) ../container-a/list-b/some-leaf
> >
> > Or is the * an allowable wildcard for a key value in a predicate ?
> >
> > I also had a question about whether the following "must" correctly
> > checks that at least one entry exists in a-list.
> >
> >   container c1 {
> >     leaf foo {
> >       must "a-list";
> >       type uint16;
> >     }
> >     list a-list {
> >       key "entry";
> >       leaf entry {
> >         type uint16;
> >       }
> >       leaf another-entry {
> >         type uint32;
> >       }
> >     }
> >   }
> >
> > I think I could also replace that must with the following:
> >       must "count(a-list) > 1";
> > but does must "a-list"; achieve the same thing ?
> >
> > Rgds,
> > Jason