ternary clarification needed

[Davide Scrimieri]

Hello,

Whenever a ternary is used are both conditions evaluated regardless ?

For example, I want to convert "my_other_var" to an object only if it is passed as as string, otherwise I don't want to touch the object, and leave it as it is.

- set_fact:

    my_var: "{{  ( my_other_var | type_debug == 'str' ) | ternary (my_other_var | from_json, my_other_var }}"

What happens right now is this:

if my_other_var is str -> It works

if my_other_var is dict -> it gives me the error saying that my_other_var should be a string to be converted from_json. But I would expect that being the condition on the left = False, it would ignore the left condition on the ternary and only consider the rightmost condition.

I also tried using when:

-- name: Set fact for string  object
  set_fact:
     my_var: "{{ my_other_var | from_json }}"
  when: (my_other_var | type_debug == 'str')
 

- name: Set fat for dict  object
  set_fact:
    my_var: "{{ my_other_var | from_json }}"

  when: (my_other_var | type_debug == 'dict')

However, if "my_other_var" is dict, the first block (named set fact for string object) gives me the same error as before. I was actually expecting that being the when statement equals to false, it would simply ignore it.

 

[Davide Scrimieri]

UPDATE: PLEASE, DISCARD what I said about the when statement at the end of my post, in my original code I had a typo, and was not working for other reasons. The first part of the post about the ternary statement still stands

[Karl Auer]

Whenever a ternary is used are both conditions evaluated regardless ?

A ternary filter consists of three parts:

a) the condition

b) the statement to be evaluated if the condition is true

c) the statement to be evaluted if the condition is false.

Only one of b) and c) will be evaluated, but the condition will always be evaluated IF the ternary statement itself is evaluated.

Regards, K.

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[Vladimir Botka]

On Wed, 25 Mar 2020 23:54:57 -0700 (PDT)
Davide Scrimieri <dscr...@redhat.com> wrote:

> I want to convert "my_other_var" to an object only if it is
> passed as as string, otherwise I don't want to touch the object, and leave
> it as it is.
>
> - set_fact:
> my_var: "{{ ( my_other_var | type_debug == 'str' ) | ternary
> (my_other_var | from_json, my_other_var }}"

I'd rather use "from_yaml". JSON is a subset of YAML. How to test types see
https://jinja.palletsprojects.com/en/master/templates/#list-of-builtin-tests

For example

vars:
my_other_var1: "'my': {'other': {'var1': 'var1'}}"
my_other_var2:
my:
other:
var2: var2

tasks:
- debug:
msg: "{{ item is string|ternary(item|from_yaml, item) }}"
loop:
- "{{ my_other_var1 }}"
- "{{ my_other_var2 }}"

gives

ok: [localhost] => (item='my': {'other': {'var1': 'var1'}}) => {
"msg": {
"my": {
"other": {
"var1": "var1"
}
}
}
}
ok: [localhost] => (item={u'my': {u'other': {u'var2': u'var2'}}}) => {
"msg": {
"my": {
"other": {
"var2": "var2"
}
}
}
}

HTH,

-vlado

[Martin Krizek]

On Thu, Mar 26, 2020 at 7:55 AM Davide Scrimieri <dscr...@redhat.com> wrote:
>
> Hello,
>
> Whenever a ternary is used are both conditions evaluated regardless ?
>
> For example, I want to convert "my_other_var" to an object only if it is passed as as string, otherwise I don't want to touch the object, and leave it as it is.
>
> - set_fact:
> my_var: "{{ ( my_other_var | type_debug == 'str' ) | ternary (my_other_var | from_json, my_other_var }}"
>

Yes, this is how the ternary filter works. To work around that you can
use a ternary statement:

- set_fact:
my_var: "{{ my_other_var | from_json if (my_other_var |
type_debug == 'str') else my_other_var }}"

That should result in desired behavior.

M.

> What happens right now is this:
>
> if my_other_var is str -> It works
> if my_other_var is dict -> it gives me the error saying that my_other_var should be a string to be converted from_json. But I would expect that being the condition on the left = False, it would ignore the left condition on the ternary and only consider the rightmost condition.
>
> I also tried using when:
>
> -- name: Set fact for string object
> set_fact:
> my_var: "{{ my_other_var | from_json }}"
> when: (my_other_var | type_debug == 'str')
>
>
> - name: Set fat for dict object
> set_fact:
> my_var: "{{ my_other_var | from_json }}"
> when: (my_other_var | type_debug == 'dict')
>
> However, if "my_other_var" is dict, the first block (named set fact for string object) gives me the same error as before. I was actually expecting that being the when statement equals to false, it would simply ignore it.
>
>

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[Davide Scrimieri]

Thank you all for the answers. I used the solution "from_yaml" provided by Vladimir and it works like a charm, and it's also cleaner. However, if this is the case, I don't believe this is an issue of how ternary works, but of how "from_json" works. My gut feeling is that it shouldn't behave that way.

To view this discussion on the web visit https://groups.google.com/d/msgid/ansible-project/CADDq2ENmBvy7%2B1rXhJ--G1c2aYDPiwJnCDU2%3D3TiC8%3D-Ergxww%40mail.gmail.com.