Re: [yang-doctors] YANG must statement constraints

On 22. 03. 21 14:44, Acee Lindem (acee) wrote:
> Hi Lada, at 
> 
> One more thing to confirm (at least for now). A predicate for a list can reference non-key items in that list - right? For example:
> 
>        list foo {
>               key "key";
>               string key;
>               string non-key;
>        }
> 
> This is still valid - correct? 
> 
>     /some/xpath/foo[non-key="acee"]

Yes, no problem. Lada

> 
> 
> Thanks,
> Acee
> 
> 
> On 3/19/21, 11:40 AM, "Ladislav Lhotka" <ladislav.lhotka@nic.cz> wrote:
> 
>     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
> 

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