How to replace only a specific entry in a nested dictionary

jean-christophe manciot

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Aug 18, 2023, 9:40:25 AM8/18/23

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The source nested dictionary is for instance the following:
vpc:
provider:
- net_type: 'db'
net_ipv4_subnet: '10.0.0.0/16'
net_ipv6_subnet: 'FD00::/64'
net_id: 0
nic_ids:
- 1111111111
- 2222222222
- net_type: 'dns'
net_ipv4_subnet: '10.1.0.0/16'
net_ipv6_subnet: 'FD01::/64'
net_id: 1
nic_ids:
- 3333333333
- 4444444444
- net_type: 'ns'
net_ipv4_subnet: '10.2.0.0/16'
net_ipv6_subnet: 'FD02::/64'
net_id: 2
nic_ids:
- 5555555555
- 6666666666

We need to replace only the whole entry indexed by "net_type: 'dns'" with:
- net_type: 'dns'
net_ipv4_subnet: '10.3.0.0/16'
net_ipv6_subnet: 'FD03::/64'
net_id: 3
nic_ids: []

so the result would look like:
vpc:
provider:
- net_type: 'db'
net_ipv4_subnet: '10.0.0.0/16'
net_ipv6_subnet: 'FD00::/64'
net_id: 0
nic_ids:
- 1111111111
- 2222222222
- net_type: 'dns'
net_ipv4_subnet: '10.3.0.0/16'
net_ipv6_subnet: 'FD03::/64'
net_id: 3
nic_ids: []
- net_type: 'ns'
net_ipv4_subnet: '10.2.0.0/16'
net_ipv6_subnet: 'FD02::/64'
net_id: 2
nic_ids:
- 5555555555
- 6666666666

I've tried the following task using the combine filter:
- name: Combining 2 <vpc> dictionaries with combine/list_merge='replace'
vars:
vpc:
provider:
- net_type: 'db'
net_ipv4_subnet: '10.0.0.0/16'
net_ipv6_subnet: 'FD00::/64'
net_id: 0
nic_ids:
- 1111111111
- 2222222222
- net_type: 'dns'
net_ipv4_subnet: '10.1.0.0/16'
net_ipv6_subnet: 'FD01::/64'
net_id: 1
nic_ids:
- 3333333333
- 4444444444
- net_type: 'ns'
net_ipv4_subnet: '10.2.0.0/16'
net_ipv6_subnet: 'FD02::/64'
net_id: 2
nic_ids:
- 5555555555
- 6666666666
net_id: 3
net_ipv4_subnet: '10.3.0.0/16'
net_ipv6_subnet: 'FD03::/64'
new_vpc: "{{ vpc | combine({'provider': [{'net_type': 'dns', 'net_id': net_id, 'net_ipv4_subnet': net_ipv4_subnet, 'net_ipv6_subnet': net_ipv6_subnet, 'nic_ids': []}]}, recursive=True, list_merge='replace') }}"
debug:
msg: "{{ new_vpc }}"

which unfortunately removes the other 2 entries:
ok: [localhost] =>
msg:
provider:
- net_id: 3
net_ipv4_subnet: 10.3.0.0/16
net_ipv6_subnet: FD03::/64
net_type: dns
nic_ids: []

Same result with community.general.lists_mergeby filter:
- name: Combining 2 <vpc> dictionaries with lists_mergeby/list_merge='replace'
vars:
vpc:
provider:
- net_type: 'db'
net_ipv4_subnet: '10.0.0.0/16'
net_ipv6_subnet: 'FD00::/64'
net_id: 0
nic_ids:
- 1111111111
- 2222222222
- net_type: 'dns'
net_ipv4_subnet: '10.1.0.0/16'
net_ipv6_subnet: 'FD01::/64'
net_id: 1
nic_ids:
- 3333333333
- 4444444444
- net_type: 'ns'
net_ipv4_subnet: '10.2.0.0/16'
net_ipv6_subnet: 'FD02::/64'
net_id: 2
nic_ids:
- 5555555555
- 6666666666
seed_vpc:
provider:
- net_type: 'dns'
net_ipv4_subnet: '10.3.0.0/16'
net_ipv6_subnet: 'FD03::/64'
net_id: 3
nic_ids: []
new_vpc: "{{ [vpc.provider, seed_vpc.provider] | community.general.lists_mergeby('net_type=dns', recursive=True, list_merge='replace') }}"
debug:
msg: "{{ new_vpc }}"

leads to:

ok: [localhost] =>
msg:
provider:
- net_id: 3
net_ipv4_subnet: 10.3.0.0/16
net_ipv6_subnet: FD03::/64
net_type: dns
nic_ids: []

Am I missing something or is it impossible to perform with the currently available ansible filters?

Todd Lewis

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Aug 18, 2023, 12:08:40 PM8/18/23

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---
- name: Replace dict in list example
  hosts: localhost
  gather_facts: false
  vars:
    vpc:
      provider:
        - net_type: 'db'
          net_ipv4_subnet: '10.0.0.0/16'
          net_ipv6_subnet: 'FD00::/64'
          net_id: 0
          nic_ids:
            - 1111111111
            - 2222222222
        - net_type: 'dns'
          net_ipv4_subnet: '10.1.0.0/16'
          net_ipv6_subnet: 'FD01::/64'
          net_id: 1
          nic_ids:
            - 3333333333
            - 4444444444
        - net_type: 'ns'
          net_ipv4_subnet: '10.2.0.0/16'
          net_ipv6_subnet: 'FD02::/64'
          net_id: 2
          nic_ids:
            - 5555555555
            - 6666666666
    fix:
      net_type: 'dns'
      net_ipv4_subnet: '10.3.0.0/16'
      net_ipv6_subnet: 'FD03::/64'
      net_id: 3
      nic_ids: []
  tasks:
    - name: Do this if the order doesn't matter
      # N.B. This assumes there is 1 provider to replace.
      ansible.builtin.debug:
        msg: "{{ item }}"
      loop:
        - "{{ [vpc.provider | selectattr('net_type', 'ne', fix.net_type)] | sum(start=[fix]) }}"

    - name: Do this if the order matters
      # N.B. This will replace _all_ "dns" providers with 'fix'.
      ansible.builtin.debug:
        msg: "{{ item }}"
      loop:
        - |
          {% set providers = [] %}
          {% for p in vpc.provider %}
          {%   set _ = providers.append(p if p.net_type != fix.net_type else fix) %}
          {% endfor %}{{ providers }}

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-- 
Todd

jean-christophe manciot

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Aug 21, 2023, 11:58:56 AM8/21/23

to Ansible Project

Very nice :-)

As it turns out, there is only one entry of type 'dns' , so both solutions work perfectly.

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