Re: [yang-doctors] YANG must statement constraints

On 19. 03. 21 16:17, Acee Lindem (acee) wrote:
> Hi Lada, 
> 
> I guess the corollary would be that: 
> 
>    must "list/non-key-leaf != 42";
> 
> Is satisfied if there is at least one list entry with a non-key-leaf other than 42.

Yes.

> 
> And,
> 
>      must not("list/non-key-leaf = 42)";
> 
> Requires all leaf entries to have non-key-leaf not equal to 42.

Yes.

> 
> What if non-key-leaf is optional and not specified? Would this be equivalent to "!= 42" in the constraint evaluation?

This is another tricky point of XPath. Either of the conditions "= 42"
and "!= 42" is satisfied only if an instance exists and satisfies the
condition. In other words, if no instance exists, then neither of the
two conditions is true.

Lada

> 
> Thanks much, 
> Acee
> 
> On 3/19/21, 11:08 AM, "Ladislav Lhotka" <ladislav.lhotka@nic.cz> wrote:
> 
>     Hi Acee,
> 
>     On 19. 03. 21 15:25, Acee Lindem (acee) wrote:
>     > When the constraint references a non-key leaf in a list, do all members
>     > of the list have to satisfy the constraint or only one of the list entries?
> 
>     It depends on how the constraint is written.
> 
>     If you have e.g.
> 
>         must "list/non-key-leaf = 42";
> 
>     then it is sufficient that at least one instance on non-key-leaf exist
>     with that value. In contrast,
> 
>         must "not(list/non-key-leaf != 42)";
> 
>     requires all instances to have that value.
> 
>     Lada
> 
>     > 
>     >  
>     > 
>     > Thanks,
>     > Acee
>     > 
>     > 
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>     > 
> 
>     -- 
>     Ladislav Lhotka
>     Head, CZ.NIC Labs
>     PGP Key ID: 0xB8F92B08A9F76C67
> 

-- 
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67