json filter in creating a jinja2 template

am trying to create my 1st jinja2 template that extracts a field from a json string as am trying to create DHCP reserveration file.

here is an example inventory feed.

I would like to select the value from the mac address to use as a value as jinja2 value for a field for the interface that matches the ansible host. which could be in any postion on the interfaces.

how would I go about it

 "TEST": {
                "ansible_host": "192.171.130.8",
                "interfaces": [
                    {
                        "ip_addresses": [
                            {
                                "address": "192.171.130.8/32",
                            }
                        ],
                        "mac_address": "C8-F1-13-78-9E-E7"
                        
                    },
                    {
                        "ip_addresses": [
                            {
                                "address": "192.171.130.80/32",
                            }
                        ],
                        "mac_address": "85-9F-76-AE-57-10"
                        
                    }
                ],
                
               
         }

so I would like to doe something like

{{ hostvars[host].interfaces.[ip_addresses.address = ansible_host].mac_address }}

but am not sure how to go about it.

This looks like a good candidate for the json_query filter. My first thought was that this should work:

hostvars[host].interfaces | json_query("[?ip_addresses[].address == '192.171.130.8/32']")

But that returns an empty list. The following is a bit more verbose, but produces the expected result:

hostvars[host].interfaces|json_query("[?ip_addresses[].address | contains(@, '192.171.130.8/32')]")

In a playbook:

- hosts: localhost
  gather_facts: false
  vars:
    TEST: {
      "ansible_host": "192.171.130.8",
      "interfaces": [
        {
          "ip_addresses": [
            {
              "address": "192.171.130.8/32",
              }
              ],
          "mac_address": "C8-F1-13-78-9E-E7"

          },
          {
            "ip_addresses": [
              {
                "address": "192.171.130.80/32",
                }
                ],
            "mac_address": "85-9F-76-AE-57-10"

            }
            ],


          }
  tasks:
    - debug:
        msg: >-
          {{ TEST.interfaces | json_query("[?ip_addresses[].address | contains(@, '192.171.130.8/32')]") }}

NB: Watch your quoting; you'll note that here I've used the YAML folding quote operating (>) because the expression contains both double quotes and single quotes, so putting either of those around the outside would mean escaping quotes inside the expression.

Running the above playbook produces:

ok: [localhost] => {
    "msg": [
        {
            "ip_addresses": [
                {
                    "address": "192.171.130.8/32"
                }
            ],
            "mac_address": "C8-F1-13-78-9E-E7"
        }
    ]
}

Since you've got the desired address in a variable (ansible_host), you would write instead:

  tasks:
    - debug:
        msg: >-
          {{
            hostvars[host].interfaces | json_query("[?ip_addresses[].address | contains(@, '%s/32')]" % ansible_host)
          }}

Our expression returns a list containing a single dictionary. If you want the mac_address field, treat the result just like any other Ansible array variable:

  tasks:
    - debug:
        msg: >-
          {{
          (
            hostvars[host].interfaces |
            json_query("[?ip_addresses[].address | contains(@, '%s/32')]" % ansible_host)
          ).0.mac_address
          }}

Create the dictionary from the MAC addresses and lists of IPs

  mac_ip_raw: "{{ dict(interfaces|json_query(mac_ip_query)) }}"
  mac_ip_query: '[].[mac_address, ip_addresses[].address]'

gives

  mac_ip_raw:
    85-9F-76-AE-57-10:
    - 192.171.130.80/32
    C8-F1-13-78-9E-E7:
    - 192.171.130.8/32

Get rid of the masks

  mac_ip: "{{ dict(mac_ip_raw.keys()|
                   zip(mac_ip_raw.values()|
                       map('map', 'split', '/')|
                       map('map', 'first'))) }}"

gives

  mac_ip:
    85-9F-76-AE-57-10:
    - 192.171.130.80
    C8-F1-13-78-9E-E7:
    - 192.171.130.8

Now, test which list contains the IP

  my_mac: "{{ mac_ip|dict2items|
              selectattr('value', 'contains', ansible_host)|
              map(attribute='key')|first }}"

gives the expected result

  my_mac: C8-F1-13-78-9E-E7

<hr>
<sup>

Example of a complete project for testing

shell> tree .
.
├── ansible.cfg
├── hosts
├── host_vars
│   └── srv1
│       └── interfaces.json
└── pb.yml

2 directories, 4 files

shell> cat ansible.cfg 
[defaults]
gathering = explicit
collections_path = $HOME/.local/lib/python3.9/site-packages/
inventory = $PWD/hosts
roles_path = $PWD/roles
retry_files_enabled = false
stdout_callback = yaml

shell> cat hosts
srv1 ansible_host=192.171.130.8

shell> cat host_vars/srv1/interfaces.json 
{
  "interfaces":
    [
        {
            "ip_addresses": [
                {
                    "address": "192.171.130.8/32"
                }
            ],
            "mac_address": "C8-F1-13-78-9E-E7"
        },
        {
            "ip_addresses": [
                {
                    "address": "192.171.130.80/32"
                }
            ],
            "mac_address": "85-9F-76-AE-57-10"
        }
    ]
}

shell> cat pb.yml 
- hosts: all

  vars:

    mac_ip_raw: "{{ dict(interfaces|json_query(mac_ip_query)) }}"
    mac_ip_query: '[].[mac_address, ip_addresses[].address]'
    mac_ip: "{{ dict(mac_ip_raw.keys()|
                     zip(mac_ip_raw.values()|
                         map('map', 'split', '/')|
                         map('map', 'first'))) }}"
    my_mac: "{{ mac_ip|dict2items|
                selectattr('value', 'contains', ansible_host)|
                map(attribute='key')|first }}"
    
  tasks:

    - debug:
        var: ansible_host
    - debug:
        var: interfaces
    - debug:
        var: mac_ip_raw
    - debug:
        var: mac_ip
    - debug:
        var: my_mac

</sup>