How to pass jinja2 variable to json_query - ansible

Question

I have the following jinja2 template
[
{% for items in hosts %}
{
"name":"{{ items.name }}",
"display_name":"{{ items.display_name }}",
"services": {{ host_group | from_json | json_query('[*].services[0]') | to_json }},
}
{% endfor %}
]
i need to replace services[0] by a variable {{ loop.index0 }}, i tried this syntax
"services": {{ host_group | from_json | json_query('[*].services[loop.index0]') | to_json }}
but i'm getting an error :
AnsibleFilterError: JMESPathError in json_query filter plugin:
Expecting: star, got: unquoted_identifier: Parse error at column 13, token "loop" (UNQUOTED_IDENTIFIER), for expression:
"[*].services[loop.index0]"
I tried another syntax:
"services": {{ host_group | from_json | json_query('[*].services[' + {{ loop.index0 }} +']') | to_json }},
and it gives also an error :
AnsibleError: template error while templating string: expected token ':', got '}'. String: [

Answer 1

There are two things to keep in mind when working with Jinja:
You never nest the {{...}} template markers.
If you put something in quotes, it's a literal string.
So when you write:
json_query('[*].services[loop.index0]')
You are passing json_query the literal string [*].services[loop.index0], which isn't a valid JMESPath query. If you want to substitute the value of a variable in a string, you need to either build the string via concatenation, or use string formatting logic.
Concatenation
Using concatenation might look like:
json_query('[*].services[' ~ loop.index0 ` ']')
Here, ~ is the string concatenation operator -- it's like +, but it makes sure to convert everything into a string. Compare this:
ansible localhost -m debug -a 'msg={{ "there are " + 4 + " lights" }}'
To this:
ansible localhost -m debug -a 'msg={{ "there are " ~ 4 ~ " lights" }}'
String formatting
Using string formatting might look like:
json_query('[*].services[%s]' % (loop.index0))
Or:
json_query('[*].services[{}]'.format(loop.index0))
These are two forms of string formatting available in Python; for more details, start here.

Answer 2

Using Ansible 2.9.23.
For the string placeholders {} and %s I had to use backticks, otherwise it wouldn't work:
json_query('results[?name==`{}`].version'.format(query))
json_query('results[?name==`%s`].version' % (query))
Given the example json:
{
(...)
"results": [
{
"envra": "0:ntp-4.2.6p5-29.el7_8.2.x86_64",
"name": "ntp",
"repo": "installed",
"epoch": "0",
"version": "4.2.6p5",
"release": "29.el7_8.2",
"yumstate": "installed",
"arch": "x86_64"
},
(...)
],
(...)
}
created by:
- name: list installed packages
yum:
list: installed
register: installed_list
with a defined variable query: ntp, pass this variable to json_query in two ways:
- name: pass var to json_query - string formatting (1)
debug:
msg: "{{ installed_list|json_query('results[?name==`{}`].version'.format(query))|first }}"
- name: pass var to json_query - string formatting (2)
debug:
msg: "{{ installed_list|json_query('results[?name==`%s`].version' % (query))|first }}"
Results:
TASK [pass var to json_query - string formatting (1)] *****************************************************************************************************
ok: [host] => {
"msg": "4.2.6p5"
}
TASK [pass var to json_query - string formatting (2)] *****************************************************************************************************
ok: [host] => {
"msg": "4.2.6p5"
}