Re: [netmod] [Netconf] What should a server response be? - depending on NP-containers

[Vladimir Vassilev <[e-mail]>]

On 08/23/2016 11:09 AM, Martin Bjorklund wrote:
> Vladimir Vassilev <[e-mail]> wrote:
>> On 08/23/2016 10:15 AM, Martin Bjorklund wrote:
>>> They are evaluated.  See Section 7.5.3:
>>>
>>>      When a datastore is validated, all "must" constraints are
>>>      conceptually evaluated once for each node in the accessible tree (see
>>>      Section 6.4.1).
>>>
>>>
>>> /martin
>> Then we have the case I objected to and the example:
>>
>> YANG 1.0:
>>
>> augment "/if:interfaces/if:interface" {
>>      container inet {
>>          must "../name = 'me0'" {
> This should have been a 'when' expression, not 'must'.  Alternatively,
> it should have been a P-container, since obviously the container has
> some semantics.  Or alternatively, the must expression should have
> been on the address leaf, since this is what you really checked.
I claim that any example of a must statement in non-presence container 
is affected in a similar way (Has anyone example that proves the 
contrary?). 'when' statements are alternative when the 'must' statement 
depends on data nodes that are not child nodes (which I admit is the 
case in this example). The thing with 'must' expressions in non-presence 
container is they are used in complicated models where 'mandatory' and 
'choice' solutions are not an option and for whatever reason the design 
got to that point the fact is that by introducing the auto-evaluation of 
non-presence containers it is even more complicated to use them. Here an 
example that stops working in YANG 1.1:

augment "/if:interfaces/if:interface" {
     container 2-company-3-crowd {
         must "(a and b and not(c)) or (not(a) and b and c) or (a and 
not(b) and c)" {
         }
         leaf a {
             type string;
         }
         leaf b {
             type string;
         }
         leaf c {
             type string;
         }
     }
}

... to make it work one has to accept to not deny the creation of 
/interfaces/interface/2-company-3-crowd as empty container and modify 
the expression adding ...or (not(a) and not(b) and not(c)).


That said I admit it is not often one needs non-presence container must 
statements. But in the cases one needs them the YANG 1.1 text is not 
helping. It causes all the statements to be processed when no one 
attempts to create them or child nodes residing in them. I find no 
justification for that.

>
>
>
> /martin
>
>
>>              description
>>                   "The inet container is only valid for the management ('me0')
>>                   interface.";
>>          }
>>          leaf address {
>>              type inet:ip-prefix;
>>          }
>>      }
>> }
>>
>> YANG 1.1 (replace "../name = 'me0'" with "../name='me0' or not
>> (./address)" and process 95 unnecessary Xpath evaluations).
>>
>> I think this proves the argument that there will be more unnecessary
>> Xpath processing.  In addition it illustrates how a simple task
>> requires ugly patch (the ".. or not (./address)" added to the must
>> expression) just to ensure the expression does not fail in the default
>> case where the interface is not named "me0" and the user has not even
>> attempted to create empty /interfaces/interface/inet container in YANG
>> 1.1.
>>
>> Vladimir
>>