Re: [yang-doctors] Yang syntax for a globally-unique key?

[Ladislav Lhotka <[e-mail]>]

Kent Watsen <[e-mail]> writes:

> Hi Lada,
>
>>>>>      Assume data model:
>>>>> 
>>>>>        +—rw tenants
>>>>>            +—rw tenant [key]
>>>>>                +—rw  key        string
>>>>>                +—rw admins
>>>>>                    +—rw admin [name]
>>>>>                         +—rw name     string
>>> <snip>
>>> I don't see any augmentation involved in either case. Anyway, I do agree
>>> that the unique statement should work. Otherwise, section 12.16 of RFC
>>> 6110 essentially gives what Kent asks for, which is in this case:
>>> 
>>>    must "not(preceding-sibling::tenant[current()/admins/admin/name])";
>> 
>> Sorry, it should be
>> 
>>    must "not(preceding-sibling::tenant[admins/admin/name  =
>> current()/admins/admin/name])
>
> I thought "preceding-sibling” was for selecting a sibling?  In my example, “tenant” doesn’t have a sibling, so what is selected?  You *are* putting the must  statement on the “tenant” node, right?

Yes. In your example, "tenant" is a list, and its instances/entries are sibling nodes in the XPath data model. So the rule states that there must not be two "tenant" entries containing admins/admin/leaf with the same value. If this condition is violated, it is reported for the second "tenant" entry.

The same rule can be written in other ways, too, but the advantage of preceding-sibling:: is that the check is performed only "above the diagonal" of all pairwise combinations of "tenant" entries.

Lada

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