Reading value using xpath : Service Reconciliation

[previousqna]

I need to read if the EFPP “negotiation” is set in the config. This configuration is either present or not present in the config… -> it does not contain an actual value.

Yang model looks like this:


Config:



In the service Reconciliation, I’m trying to read its value like this:

auto_negotiation_path = "/ncs:devices/device[name=’Pf-9k-01']/config/cisco-ios-xr:interface/GigabitEthernet[id='0/0/0/12']/negotiation/auto";

The function maapi.xpathEvalExpr is always returning empty, regardless of the present/absence of negotiation in the config. (I tried several variations like trying to read into a Boolean, different xpath’s, adding prefix,…)

Did anyone faced this issue before?

[previousqna]

Try to use this command:

show configuration devices device Pf-9k-01 config cisco-ios-xr:interface GigabitEthernet 0/0/0/12 | display xpath

You will get all the xpath possibilities.

It seems to me that you should get the value of “/ncs:devices/device[name=’Pf-9k-01']/config/cisco-ios-xr:interface/GigabitEthernet[id='0/0/0/12']/negotiation”.

[previousqna]

It does not contain an actual value like the others.

The config either it’s there or not there.

I tried using:
“/ncs:devices/device[name=’Pf-9k-01']/config/cisco-ios-xr:interface/GigabitEthernet[id='0/0/0/12']/negotiation”.
Returns always empty.

[previousqna]

The path seems to be correct:

admin@ncs> config

Entering configuration mode private

[ok][2016-04-19 12:58:07]

[edit]

admin@ncs% set devices device XRv9K_CASLAB-01 config cisco-ios-xr:interface GigabitEthernet 0/0/0/6 negotiation auto

[ok][2016-04-19 12:58:10]

[edit]

admin@ncs% commit

Commit complete.

[ok][2016-04-19 12:58:19]

[edit]

admin@ncs% exit    

[ok][2016-04-19 12:58:31]

admin@ncs> show configuration devices device XRv9K_CASLAB-01 config cisco-ios-xr:interface GigabitEthernet 0/0/0/6

negotiation {

    auto;

}

[ok][2016-04-19 12:58:37]

admin@ncs> show configuration devices device XRv9K_CASLAB-01 config cisco-ios-xr:interface GigabitEthernet 0/0/0/6 | display xpath

/devices/device[name='XRv9K_CASLAB-01']/config/cisco-ios-xr:interface/GigabitEthernet[id='0/0/0/6']/negotiation/auto

[ok][2016-04-19 12:58:43]

The REST NBI seems to return different values for configured interfaces (Gi0/0/0/6) and not configured interfaces (Gi0/0/0/5):

Gi0/0/0/6:

[ncsdev@ncs ~]$ curl -uadmin:admin -X GET -H "Accept: application/vnd.yang.data+json"http://localhost:8080/api/running/devices/device/XRv9K_CASLAB-01/config/cisco-ios-xr:interface/GigabitEthernet/0%2F0%2F0%2F6/negotiation

{

  "tailf-ned-cisco-ios-xr:negotiation": {

    "auto": {

    }

  }

}

[ncsdev@ncs ~]$ curl -uadmin:admin -X GET -H "Accept: application/vnd.yang.data+json"http://localhost:8080/api/running/devices/device/XRv9K_CASLAB-01/config/cisco-ios-xr:interface/GigabitEthernet/0%2F0%2F0%2F6/negotiation/auto

{

  "tailf-ned-cisco-ios-xr:auto": {

  }

}

Gi0/0/0/5:

[ncsdev@ncs ~]$ curl -uadmin:admin -X GET -H "Accept: application/vnd.yang.data+json"http://localhost:8080/api/running/devices/device/XRv9K_CASLAB-01/config/cisco-ios-xr:interface/GigabitEthernet/0%2F0%2F0%2F5/negotiation/auto

[previousqna]

If you want to retrieve something, you should be using the getElem method and not xpathEvalExpr, shouldn’t you?

[previousqna · Accepted solution]

an XPath expression returns an XPath value, string, number, boolean or date. You just select a node with no content.

To illustrate I will use the ncs_cmd utility using the 'xe' command, short for XPath Expression:

» ncs_cmd -c "xe /devices/device[name='ios0']/config/ios:router/bgp/as-no"

64512

This returns the text representation of the node as-no, we can also write explicitly:

» ncs_cmd -c "xe /devices/device[name='ios0']/config/ios:router/bgp/as-no/text()"

64512

Selecting a node with no content will yield an empty result:

» ncs_cmd -c "xe /devices/device[name='ios0']/config/ios:router/bgp/bgp"

We are in fact selecting a node it just do not have any content, verify with the XPath function count()

» ncs_cmd -c "xe count(/devices/device[name='ios0']/config/ios:router/bgp/bgp)"

1

What you want is to test if something exists or not, an empty node-set is always false, a non-empty is always true.

You can testthat by using the XPath function boolean():

» ncs_cmd -c "xe boolean(/devices/device[name='ios0']/config/ios:router/bgp[as-no=64512])"

true

» ncs_cmd -c "xe boolean(/devices/device[name='ios0']/config/ios:router/bgp[as-no=64513])"

false

For more one XPath please consult:https://www.w3.org/TR/xpath/