INVALID_HIERARCHY_PARENT error

Trying to use Python to print out the result of a CRUD read in xml format. The following works perfectly: 

from ydk.models.cisco_ios_xr import Cisco_IOS_XR_l2vpn_oper as L2VpnOper

def get_xconnect(provider, crud):

    base_obj = L2VpnOper.L2Vpn.Xconnects.Xconnect()

    base_data = crud.read(provider, base_obj) 

When the value of “base_obj”  is changed to the following, a proper read request is sent but getting a timeout (possibly because the resulting object has too much information to populate in the allotted time – is this the case.):

def get_xconnect(provider, crud):

    base_obj = L2VpnOper.L2VpnForwarding.Nodes.Node()

    base_data = crud.read(provider, base_obj) 

output:

READ operation initiated 

<rpc xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" message-id="urn:uuid:a18cbaf9-c8b9-4af9-b775-08ee13c96a62">

  <get>

    <filter type="subtree">

      <l2vpn-forwarding xmlns="http://cisco.com/ns/yang/Cisco-IOS-XR-l2vpn-oper">

        <nodes>

          <node/>

        </nodes>

      </l2vpn-forwarding>

    </filter>

  </get>

</rpc>

after some time …

READ operation completed

Traceback (most recent call last):

. . .

. . .

  File "/auto/cafy_dev/cafykit/exec/lib/python3.4/site-packages/ncclient/operations/rpc.py", line 345, in _request

    raise TimeoutExpiredError('ncclient timed out while waiting for an rpc reply.')

ncclient.operations.errors.TimeoutExpiredError: ncclient timed out while waiting for an rpc reply. 

Tried to initialize “base_obj” to a child class of L2VpnForwarding.Nodes.Node to see if the timeout would still occur, but got an INVALID_HIERARCHY_PARENT error instead. 

def get_xconnect(provider, crud):

    base_obj = L2VpnOper.L2VpnForwarding.Nodes.Node.L2FibBridgeDomains.L2FibBridgeDomain()

    base_data = crud.read(provider, base_obj) 

output:

READ operation initiated

YPYErrorCode.INVALID_HIERARCHY_PARENT

READ operation completed

Traceback (most recent call last):

  File "mpls_te_demo.py", line 588, in <module>

    get_xconnect_output = get_xconnect(provider, crud)

  File "mpls_te_demo.py", line 466, in get_xconnect

    base_data = crud.read(provider, base_obj)

  File "/auto/cafy_dev/cafykit/exec/lib/python3.4/site-packages/ydk/services/crud_service.py", line 150, in read

    payload = self._execute_crud_operation_on_provider(provider, read_filter, 'READ', only_config)

  File "/auto/cafy_dev/cafykit/exec/lib/python3.4/site-packages/ydk/services/crud_service.py", line 166, in _execute_crud_operation_on_provider

    self._raise_parent_hierarchy_error()

  File "/auto/cafy_dev/cafykit/exec/lib/python3.4/site-packages/ydk/providers/_provider_plugin.py", line 520, in _raise_parent_hierarchy_error

    raise YPYServiceProviderError(error_code=YPYErrorCode.INVALID_HIERARCHY_PARENT)

ydk.errors.YPYServiceProviderError: Parent is not set.                    

Parent Hierarchy cannot be determined. 

This has happened with every child class of L2VpnForwarding.Nodes.Node . Copied straight from the YDK documentation, so the class names are correct. 

How to deal with this INVALID_HIERARCHY_PARENT error..

    provider = NetconfServiceProvider(address=10.0.0.1,
                                      port=830,
                                      username='admin',
                                      password='admin',
                                      protocol='ssh',
                                      timeout=120)

ydk.errors.YPYServiceProviderError: Parent is not set.                     Parent Hierarchy cannot be determined

It seems like it complains about missing key value for L2VpnOper.L2VpnForwarding.Nodes.Node. Maybe an issue related to #399.

A related discussion could be found here.

And as suggested in the issue and the discussion, you might need to instantiate L2VpnForwarding.Nodes.Node and append base_obj to the corresponding attribute for this object.