[yang-doctors] A compact way to compare a type in YANG

[Scott Mansfield <[e-mail]>]

Yang Doctors,

 

The IEEE has been working on the IEEE 802.1 bridge model and while updating
some when statements in  YANG models ieee802-dot1q-bridge and
ieee802-dot1q-pb to select conditions for certain types of bridge components
we had a question. 

 

The pertinent part of the bridge tree is this:

 

module: ieee802-dot1q-bridge

  +--rw bridges

     +--rw bridge* [name]

        +--rw name           dot1qtypes:name-type

        +--rw address        ieee:mac-address

        +--rw bridge-type    identityref

        +--ro ports?         uint16

        +--ro up-time?       yang:zero-based-counter32

        +--ro components?    uint32

        +--rw component* [name]

           +--rw name                     string

           +--rw id?                      uint32

           +--rw type                     identityref <- This is the type we
want to test.

           +--rw address?                 ieee:mac-address

 

 

 

And later in the same file an augmented interface tree looks like  this:

 

 

augment /if:interfaces/if:interface:

    +--rw bridge-port

       +--rw bridge-name?                           -> /bridges/bridge/name

       +--rw component-name?                        ->
/bridges/bridge[dot1q:name=current()/../bridge-name]/component/name

 

 

In several places we are using a when statement with an xpath condition
while in the interface tree context: (This is what it looks like in the
ieee802-dot1q-pb module)

when

 
"/dot1q:bridges/dot1q:bridge[dot1q:name=current()/../dot1q:bridge-name]/dot1
q:component[dot1q:name=current()/../dot1q:component-name]/dot1q:type =
'dot1q:c-vlan-component'

 

We had a discussion on our Yangsters meeting this seem rather cumbersome and
whether the component type value could be locally instantiated with the
value of the respective component type to reduce the when statement to: 

 

when " ../dot1q:component-type = 'dot1q:c-vlan-component' "

 

The suggestion was adding this:

 

      leaf component-type {

        type leafref {

          path
"/dot1q:bridges/dot1q:bridge[dot1q:name=current()/../bridge-name]/dot1q:comp
onent[dot1q:name=current()/../component-name]/dot1q:type";  

        }

        description

          "Used to reference the Component type.";

      }

 

However I don't think this works it seems to only make the leafref type of
component-type the same as the dot1q type of ../component/type which is an
identityref. (type-of-component) . Other attempts to make this work failed
too.

 

Does YANG offer another mechanism for a more compact form to do what we
want? 

 

Thanks for your consideration!

 

Regards,

-scott.