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

[Kent Watsen <[e-mail]>]

>> Pyang validated the corrected expression above, but yanglint threw an error, as described by: https://github.com/CESNET/libyang/issues/1180 <https://github.com/CESNET/libyang/issues/1180>.
> 
> Yes, we discussed this with Michal previously. The fact that there is no specific prescribed order doesn't mean there is no order at all. XPath data model expects the siglings to be in a sequence.

Michael says that he’ll schedule it for near end-of-year, in yanglint 2.0 only.


>> I have not yet tested with Yangson.  Is it known if Yangson supports "preceding-sibling”?  Looking at https://yangson.labs.nic.cz/xpath.html <https://yangson.labs.nic.cz/xpath.html> I see this:
>> 
>>    NotSupported – if the input XPath expression contains a feature that
>>    isn’t supported by the implementation, such as the preceding:: axis.
> 
> Yangson does support it, see below. Of course, preceding:: axis really makes no sense with YANG-modelled data.

Oh, happy days  :)

To workaround the yanglint issue, I guess that code can dynamically add a new “must” expression to an instance of Yangson’s “SchemaNode” class here: https://yangson.labs.nic.cz/schemanode.html#yangson.schemanode.SchemaNode.must <https://yangson.labs.nic.cz/schemanode.html#yangson.schemanode.SchemaNode.must>.

K.

> Lada
> 
> (yangson) $ cat test.yang 
> module test {
>  yang-version 1.1;
>  namespace "https://example.net/test";
>  prefix "t";
> 
>  container tenants {
>    list tenant {
>      key key;
>      must "not(preceding-sibling::tenant[admins/admin/name = current()/admins/admin/name])";
>      leaf key {
>        type string;
>      }
>      container admins {
>        list admin {
>          key name;
>          leaf name {
>            type string;
>          }
>        }
>      }
>    }
>  }
> }
> 
> (yangson) $ cat ylib.json 
> {
>  "ietf-yang-library:modules-state": {
>    "module-set-id": "",
>    "module": [
>      {
>        "name": "test",
>        "revision": "",
>        "namespace": "https://example.net/test",
>        "conformance-type": "implement"
>      }
>    ]
>  }
> }
> (yangson) $ cat inst1.json 
> {
>    "test:tenants": {
> 	"tenant": [
> 	    {
> 		"key": "foo",
> 		"admins": {
> 		    "admin": [ { "name": "alice" } ]
> 		}
> 	    },
> 	    {
> 		"key": "bar",
> 		"admins": {
> 		    "admin": [ { "name": "bob" } ]
> 		}
> 	    }
>        ]
>    }
> }
> 
> (yangson) $ cat inst2.json 
> {
>    "test:tenants": {
> 	"tenant": [
> 	    {
> 		"key": "foo",
> 		"admins": {
> 		    "admin": [ { "name": "alice" } ]
> 		}
> 	    },
> 	    {
> 		"key": "bar",
> 		"admins": {
> 		    "admin": [ { "name": "alice" } ]
> 		}
> 	    }
>        ]
>    }
> }
> 
> (yangson) $ yangson -v inst1.json ylib.json 
> (yangson) $ yangson -v inst2.json ylib.json 
> Semantic error: [/test:tenants/tenant/1] must-violation
> 
> -- 
> Ladislav Lhotka 
> Head, CZ.NIC Labs
> PGP Key ID: 0xB8F92B08A9F76C67
> 
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