How can I traverse nested lists in Ansible? - ansible

Question

I have a list of devices, each of which has a varying list of attributes that must be created on the devices, one at a time. Is there a way to build a nested set of loops to do this? The with_nested construct applies every attribute to every device; I need only a single attribute per device per call.
This playbook demonstrates what I have tried (Ansible 2.7.1, Python 2.7.1):
- name: Test nested list traversal
hosts: localhost
connection: local
vars:
Stuff:
- Name: DeviceA
Info: AInfo
Values:
- ValueA1
- ValueA2
- Name: DeviceB
Info: BInfo
Values:
- ValueB1
- ValueB2
- ValueB3
tasks:
- name: Loop test
debug:
msg: "{{ item.Name }},{{ item.Info }}, {{ item.Values }}"
with_items:
- "{{ Stuff }}"
What I get: (One call per device, containing all attributes at once)
ok: [localhost] => (item={u'Info': u'AInfo', u'Values': [u'ValueA1', u'ValueA2'], u'Name': u'DeviceA'}) =>
msg: DeviceA,AInfo, [u'ValueA1', u'ValueA2']
ok: [localhost] => (item={u'Info': u'BInfo', u'Values': [u'ValueB1', u'ValueB2', u'ValueB3'], u'Name': u'DeviceB'}) =>
msg: DeviceB,BInfo, [u'ValueB1', u'ValueB2', u'ValueB3']
What I want (each msg represents a separate operation to be performed on the device with just that one attribute)
msg: DeviceA, AInfo, ValueA1
msg: DeviceA, AInfo, ValueA2
msg: DeviceB, BInfo, ValueB1
msg: DeviceB, BInfo, ValueB2
msg: DeviceB, BInfo, ValueB3

Answer 1

You can get what you want using the subelements filter:
---
- hosts: localhost
gather_facts: false
vars:
Stuff:
- Name: DeviceA
Info: AInfo
Values:
- ValueA1
- ValueA2
- Name: DeviceB
Info: BInfo
Values:
- ValueB1
- ValueB2
- ValueB3
tasks:
- debug:
msg: "{{ item.0.Name }}, {{ item.0.Info }}, {{ item.1 }}"
loop: "{{ Stuff|subelements('Values') }}"
loop_control:
label: "{{ item.0.Name }}"
Running the above playbook gets you:
PLAY [localhost] ******************************************************************************************************************************************************************************
TASK [debug] **********************************************************************************************************************************************************************************
ok: [localhost] => (item=DeviceA) => {
"msg": "DeviceA, AInfo, ValueA1"
}
ok: [localhost] => (item=DeviceA) => {
"msg": "DeviceA, AInfo, ValueA2"
}
ok: [localhost] => (item=DeviceB) => {
"msg": "DeviceB, BInfo, ValueB1"
}
ok: [localhost] => (item=DeviceB) => {
"msg": "DeviceB, BInfo, ValueB2"
}
ok: [localhost] => (item=DeviceB) => {
"msg": "DeviceB, BInfo, ValueB3"
}
PLAY RECAP ************************************************************************************************************************************************************************************
localhost : ok=1 changed=0 unreachable=0 failed=0