Iterating via nested loops - ansible

Question

The packages.yml file defined as:
---
- packages:
- name: Some description 1,
packageList:
- package1,
- package2,
- package3
- name: Some description 2,
package: package4
The first item contains a field packageList, the 2nd item does not have it, but only package field.
Playbook:
---
- hosts: all
become: yes
vars_files:
- packages.yml
How to iterate via all packageList items of the packages list only if this packageList is defined for an item.
Here is how I can iterate through items which contain package field:
- name: iteration
debug:
msg: "name: {{ item.package }}"
when: item.package is defined
with_items: "{{ packages }}"

Answer 1

As noted in my comment, if you simply want to install multiple yum/apt packages, it is usually more efficient to simply pass the list to the apt/yum/package module. As the docs state:
"When used with a loop: each package will be processed individually, it is much more efficient to pass the list directly to the name option."
However, if you really need a loop, here is a possible solution:
playbook.yml:
---
- hosts: all
gather_facts: false
vars_files:
- packages.yml
tasks:
- name: iteration over single items
debug:
msg: "name: {{ item.package }}"
when: item.package is defined
with_items: "{{ packages }}"
- name: iteration over lists
debug:
msg: "name: {{ item.packageList }}"
when: item.packageList is defined
with_items: "{{ packages }}"
- name: Do something with individual packages in the list
include_tasks: process_list.yml
vars:
mylist: "{{outer.packageList}}"
when: outer.packageList is defined
loop: "{{ packages }}"
loop_control:
loop_var: outer
process_list.yml:
- name: See what we have received
debug:
var: item
loop: "{{mylist}}"
result:
PLAY [all] *******************************************************************************************************************************
TASK [iteration over single items] *******************************************************************************************************
skipping: [localhost] => (item={u'packageList': [u'package1,', u'package2,', u'package3'], u'name': u'Some description 1,'})
ok: [localhost] => (item={u'name': u'Some description 2,', u'package': u'package4'}) => {
"msg": "name: package4"
}
TASK [iteration over lists] **************************************************************************************************************
ok: [localhost] => (item={u'packageList': [u'package1,', u'package2,', u'package3'], u'name': u'Some description 1,'}) => {
"msg": "name: [u'package1,', u'package2,', u'package3']"
}
skipping: [localhost] => (item={u'name': u'Some description 2,', u'package': u'package4'})
TASK [Do something with individual packages in the list] *********************************************************************************
skipping: [localhost] => (item={u'name': u'Some description 2,', u'package': u'package4'})
included: /root/tmp/process_list.yml for localhost
TASK [See what we have received] *********************************************************************************************************
ok: [localhost] => (item=package1,) => {
"ansible_loop_var": "item",
"item": "package1,"
}
ok: [localhost] => (item=package2,) => {
"ansible_loop_var": "item",
"item": "package2,"
}
ok: [localhost] => (item=package3) => {
"ansible_loop_var": "item",
"item": "package3"
}
PLAY RECAP *******************************************************************************************************************************
localhost : ok=4 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
The loop_control/loop_var part is used because otherwise both the outer and inner loop will use {{item}} as the loop variable - and this will cause... interesting results :)

Answer 2

You can define a default value with an empty list for the cases, where the packageList is undefined.
{{ item.packageList | default ([]) }}
If the packageList is undefined, the job iterates over an empty list, which means, it does not do anything.

Answer 3

You can use default, as #ceving mentioned:
---
- hosts: localhost
connection: local
vars_files:
- packages.yml
tasks:
- name: iteration
debug:
msg: "name: {{ item.packageList | default([item.package]) }}"
with_items: "{{ packages }}"
If packageList exists, it will use that, else package put into a single-element array to match the form of packageList:
PLAY [localhost] **********************************************************************************************
TASK [Gathering Facts] ****************************************************************************************
ok: [localhost]
TASK [iteration] **********************************************************************************************
ok: [localhost] => (item=None) => {
"msg": "name: [u'package1,', u'package2,', u'package3']"
}
ok: [localhost] => (item=None) => {
"msg": "name: [u'package4']"
}
PLAY RECAP ****************************************************************************************************
localhost : ok=2 changed=0 unreachable=0 failed=0