Re: [netmod] a question about 'when'

On Mon, Aug 5, 2019 at 2:49 AM Ladislav Lhotka <lhotka@nic.cz> wrote:

> "Fengchong (frank)" <frank.fengchong@huawei.com> writes:
>
> > Hi all,
> >
> > I encounter a question about 'when', when I implement yang model
> associated when condition.
> >
> > Yang model:
> >
> > leaf password-type {
> >    type enumeration {
> >       enum null;
> >       enum simple;
> >       enum cipher;
> >    }
> > }
> >
> > leaf password-text {
> > type string;
> > when "../password-type != null";
> > }
> >
> > I config these two leafs as below:
> > <password-type>simple</password-type>
> > <password-text>123456</password-text>
> >
> > And I changed password-type to null, I get the config like below:
> > <password-type>null</password-type>
> >
> > And then, I reconfig the password-type to simple, what data should be
> returned?
> >
> > Is
> >   <password-type>simple</password-type>
>
> According to RFC 7950, sec. 8.2, the server deleted "password-text" after
> you changed "password-type" to null but the original value isn't recovered
> after you change the type back.
>
> This server behaviour means that a typo or similar trivial error may have
> catastrophic consequences such as auto-deletion of entire configuration
> subtrees. That's why our RESTCONF implementation (jetconf) does something
> else: it won't permit you to change "password-type" to null as long as the
> "password-text" exists.
>
>
It seems odd to optimize the server for client mistakes.
It is far more likely (99 to 1?) that the client knows what it is doing and
expects
the standard to be followed.  Consider the burden on the client deleting all
the "false-when" nodes manually.  This is also inconsistent with the
standard
behavior for choice-stmt (new case deletes the old case automatically).

Lada
>
>
Andy

> >
> > Or
> >
> >   <password-type>simple</password-type>
> >   <password-text>123456</password-type>
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>
> --
> Ladislav Lhotka
> Head, CZ.NIC Labs
> PGP Key ID: 0xB8F92B08A9F76C67
>
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