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

[Martin Bjorklund <[e-mail]>]

"Sterne, Jason (Nokia - CA/Ottawa)" <[e-mail]> wrote:
> Thx.  In the case I'm most concerned about, a-list (and all
> descendants) is config true and 'entry' is the key leaf.

No need to check for a key's existance!

> 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

Yes.  As would:

    must "../a-list[1=1]/entry";
    must "../a-list[count(*) > 0]/entry";

etc; if you want to have a confusing expression instead of the simple:

    must "../a-list";


/martin



> 
> 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