I wish I could just put static_leases: "{{ dhcp_reservations }}" in the host’s variables and call it a day, but that won’t work obviously.
I’m not at liberty to alter or edit one of these roles, so I have at least one case where I can’t change the task that uses these variables to fit the dictionary keys being used already.
How can I/should I transform the name of these dictionary keys on each item in the list while preserving the value? Alternatively, how can I add a new dictionary key with the needed name and the same value?
I tried going through Ansible documentation, filters, etc, but couldn’t seem to find a solution that worked with dictionary keys on list items.
I apologize for not giving more concrete examples of what I tried, but I haven’t touched it over the weekend, and it became all a blur.
Can’t shake the feeling that the answer is simple, and I’m just overlooking something obvious.
I appreciate any solutions people might have.
Someone brighter than me might be able to do this without a loop, perhaps using map or json_query / JMESPath or something but I’d do it the slow and simple way with a loop through the original list to create a new list, something like this (untested!)
- name: Set a fact for the AdGuard Home static leases
ansible.builtin.set_fact:
adguard_list: "{{ adguard_list | default([]) + adguard_item }}"
vars:
adguard_item: |
{
"mac": "{{ dhcp_reservation.mac_address }}",
"ip": "{{ dhcp_reservation.number }}",
"hostname": "{{ dhcp_reservation.name }}"
}
loop: dhcp_reservations
loop_control:
loop_var: dhcp_reservation
- name: Print the AdGuard Home static leases list
ansible.builtin.debug:
var: adguard_list
I have definitely tried a few things involving map().
I was hoping that I wouldn’t have to run some pre_tasks in the playbook just to get this to work, but it is a good simplistic interim solution.
I’ll keep it in mind for sure.
Try using JMESPath (which needs to be installed on the Ansible controller), I think this will work,
- name: Set a fact for the AdGuard Home static leases
ansible.builtin.set_fact:
adguard_list: "{{ dhcp_reservations | community.general.json_query('[].{mac: mac_address, ip: number, hostname: name}') }}"
- name: Print the AdGuard Home static leases list
ansible.builtin.debug:
var: adguard_list
You could skip the fact setting step if you want and use the above as the body for the uri module.
I find the JMESPath Terminal really handy for working out queries like this:
Each of the number dictionary keys also needs its value transformed/filtered into an actual IP address, but that is a separate and different problem I believe.
That Jinja is so broken ill-designed that it can’t do things out-of-the box that are so easily done by jmespath, jq, etc. is disappointing. But what truly makes me sad is that Ansible (which I care about a lot) is saddled with Jinja (which I have no need for outside of Ansible).
I understand how this came to be. Incorporating Jinja must have saved a lot of development effort when Ansible was in its formative years. And strictly as a templating tool Jinja is arguably adequate.
But Ansible and its users deserve a data expression language worthy of the challenges that Jinja studiously avoids rising to. I can envision a drop-in replacement that handles all current valid Jinja expressions, but that integrates better with Ansible (fully qualified variables anyone?) while not shying away from real power.
The first target on my list would be the “map” filter. In addition to the currently accepted special case keywords and its fixed list of filters (which ironically includes “map” itself) , it should also accept arbitrarily complex expressions. “map” is supposed to be the pipeline’s answer to loops, but why limit what you can do in those loops to a short list of anticipated operations? The OP’s problem could be solved without having to resort to outside libraries if “map” weren’t thus hobbled.
I’m not ranting at you, @chris; I’m just generically ranting. It landed here because I wasted a couple of hours trying to solve this problem using built-in tools. It’s not the first time I’ve set off on this fool’s errand either, so I should have known better. Should not have to pull in extra libraries. Or create a custom filter in python. This should be possible, nay practical, to solve this using the built-in data manipulation language. But we’re stuck with Jinja.
— “I’m looking at you, Jinja! I’m calling you out!”
The JMESPath answer seems fairly efficient to me :
I’ve found JMESPath easier to learn than Jinja because of the associated tools, jp and jpterm and the fact that it’s an extra library doesn’t really bother me…
In fact I like the fact that Ansible can use other libraries like JMESPath, another favourite of mine is JC which can be used via the community.general.jc filter.
I would however be very interested in seeing your ideas and suggestions being worked on and developed further @utoddl .
All I had to do is pass it through the filter like so: "{{ dhcp_reservations | ansible.utils.replace_keys(target=[{'before': 'mac_address', 'after': 'mac'}, {'before': 'number', 'after': 'ip'}, {'before': 'name', 'after': 'hostname'}]) }}"
And the desired result is achieved. grumbles about having looked over that list of filters a dozen times over
:
.