defaulting on undefined nested dictionaries

[Patrick McMahon]

Hi all,

I have a dictionary with a nested dictionary defined in defaults/main.yml of my role:

file_system_system_vg:
  name: "A Name"
  lv: {}

where lv is the nested dictionary.

I can use the nested dictionary in a task like this:

- name: Create Logicals Volumes on primary VG
  lvol: vg={{ file_system_system_vg.name }} lv={{ item.value.name }} size={{ item.value.size }}
  with_dict: file_system_system_vg.lv

This all works fine when file_system_system_vg is defined, but i would like to remove it from defaults/main.yml and only run the task when file_system_system_vg.lv is defined elsewhere, so I have tried this:

- name: Create Logicals Volumes on primary VG
  lvol: vg={{ file_system_system_vg.name }} lv={{ item.value.name }} size={{ item.value.size }}
  with_dict: file_system_system_vg.lv | default ({})

but it throws an error:

TASK: [file_system | Create Logicals Volumes on primary VG] *******************
fatal: [dsdptgfc06v.devqa.exch.int] => with_dict expects a dict

Please note that file_system_system_vg is not defined here and neither is file_system_system_vg.lv. Does this make sense?
How can I make ansible skip this task when both file_system_system_vg and file_system_system_vg.lv are undefined?
N.B when I run the task I need to use the dictionaries within file_system_system_vg.lv

Thanks in advance
Paddy


[Brian Coca]

have you tried:

with_dict: "{{ file_system_system_vg is
defined|ternary(file_system_system_vg.lv|default({}), {})}}"

?

--
Brian Coca

[Patrick McMahon]

Hi Brian,

so in my defaults/main.yml if I define only this:

file_system_system_vg:

It works! so we are nearly there. If I remove file_system_system_vg from defaults/main.yml it throws an error again:

TASK: [file_system | Create Logicals Volumes on primary VG] *******************
fatal: [dsdptgfc06v.devqa.exch.int] =>

with_dict expects a dict

PLAY RECAP *******************************************************************

So is it possible to remove file_system_system_vg completely from defaults/main.yml?

Thanks
Patrick

[Patrick McMahon]

I made a simple playbook to show the issue. It seems ansible evalutes all variables regardless of the conditional result before ternary.
If you run the playbook twice, once with "simpleDict" defined, and again with it commented out.

---
#TESTING: ternary behaviour
- name: Run - Testing ternary
  sudo: yes
  hosts: "{{hosts}}"
  gather_facts: no

  vars:
    simpleDict:
    #  name: 'A simple dictionary'
    #  nestedDict: {}

  tasks:
    - set_fact: foo="{{ simpleDict is defined | ternary(simpleDict.nestedDict|default({}),"simpleDict not defined") }}"

    - debug: var=foo

Thanks
Patrick

[Christian Thiemann]

You can specify default values for both the dictionary in which you are trying to look something up, and the key you are looking up:

  with_dict: (file_system_system_vg|default({})).lv|default({})

The parentheses are important!

[Patrick McMahon]

It works, exactly what I was after! Thanks Christian

Patrick