Question:What's the function of 'key' in PathElem define? about gnmi

[aashaikh]

Please see the explanation in the gNMI spec: https://github.com/openconfig/reference/blob/master/rpc/gnmi/gnmi-specification.md#222-paths

The key map is used to express a path element that requires one or more index values, such as a list in YANG:
/interfaces/interface[name=eth0]/state/oper-status

The second path element requires use of the key. There are examples of the encoding at the link above.

[dingrui37]

Thank you for your reply . I think what you mean is like below, is it right?
For example, "/interfaces/interface[name=eth0]"

string name = 1;             -----------> name = "/interfaces/interface"
map<string, string> key = 2; ----------->  key = "name", value  = "eth0"

Why not use the full xpath string directly, just like "/interfaces/interface[name=eth0]"? I want to ask another question. If the path is "/interfaces/interface[name=eth0]/state/oper-status", the name field is
"/interfaces/interface/state/oper-status" or "/interfaces/interface[name=eth0]/state/oper-status"? and the key is null?

[robshakir]

We've iterated on the path specification a number of times -- the motivation for this format is that it is significantly simpler to work with than having string parsing throughout the code. The full proposal and discussion that Marcus, Carl, Anees and I put together is in this issue. You can see the discussion there.

The name field is a repeated -- so your example isn't correct, again please see the examples. This would be encoded using multiple PathElem messages, i.e.:

elem: <
  name: "interfaces"
>
elem: <
  name: "interface"
  key: <
    key: "name"
    value: "eth0"
  >
>

The second example just appends more elem entries onto the end of the repeated:

elem: <
  name: "interfaces"
>
elem: <
  name: "interface"
  key: <
    key: "name"
    value: "eth0"
  >
>
elem: <
 name: "state"
>
elem: <
  name: "oper-status"
>

(Using standard Go textproto encoding format)

In the case that there are no keys (i.e., an element is not a YANG list, if using YANG) then the key map is null.

[dingrui37]

Thanks @robshakir. I overlooked that the name field is a repeated, I think I have already understood.