How to extract a list of values of a field within a list of dictionaries when a key matches another list of values

jean-christophe manciot

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Feb 5, 2022, 9:56:36 AM2/5/22

to Ansible Project

Let's assume the following fictional list of dictionaries:

domain_definition:
- name: server11
cluster: cluster1
db_servers:
- server12
- server21
port: '8080'
- name: server12
cluster: cluster1
db_servers:
- server22
port: '8090'
- name: server13
cluster: cluster1
port: '8091'
- name: server21
cluster: cluster2
db_servers:
- server12
- server22
port: '9080'
- name: server22
cluster: cluster2
port: '9090'

The goal is to list all ports of used 'db_servers', so the expected list is:

- '8090'
- '9080'
- '9090'
- '8090'
- '9090'

The constraint is to use one (some operation is performed for each item) and only one loop (the list is huge in reality).

The following does not work because selectattr expects a value, not a list of values:

- name: Extracting a list of values of a field within a list of dictionaries when a key matches another list of values
hosts:
- localhost
strategy: debug
tasks:
- name: Extracting a list of values of a field within a list of dictionaries when a key matches another list of values
vars:
domain_definition:
- name: server11
cluster: cluster1
db_servers:
- server12
- server21
port: '8080'
- name: server12
cluster: cluster1
db_servers:
- server22
port: '8090'
- name: server13
cluster: cluster1
port: '8091'
- name: server21
cluster: cluster2
db_servers:
- server12
- server22
port: '9080'
- name: server22
cluster: cluster2
port: '9090'
db_servers_names: "{{ item.db_servers |
default([]) |
list }}"
db_servers_used_ports: "{{ domain_definition |
selectattr('name', 'eq', db_servers_names) |
map(attribute= 'port') |
list }}"
debug:
msg:
- "db_servers_names: {{ db_servers_names }}"
- "db_servers_used_ports: {{ db_servers_used_ports }}"
loop: "{{ domain_definition }}"

Any suggestion?

Todd Lewis

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Feb 6, 2022, 6:25:26 PM2/6/22

to Ansible Project

Instead of

selectattr('name', 'eq', db_servers_names)

try this:

selectattr('name', 'in', db_servers_names)

Todd Lewis

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Feb 6, 2022, 8:32:38 PM2/6/22

to ansible...@googlegroups.com, jean-christophe manciot

This produces the list you want:

---
- name: Extracting a list of values of a field within a list of dictionaries when a key matches another list of values
  hosts:
    - localhost
  strategy: debug
  tasks:
    - name: Extract a list of values of a field within a list of dictionaries when a key matches another list of values
      set_fact:
        db_used_ports: |
            {% set ports=[] %}
            {% for dd0 in domain_definition %}
            {%   set db_servers_names=dd0.db_servers|default([]) %}
            {%   for dd1 in domain_definition %}
            {%     if dd1['name'] in db_servers_names %}
            {%       set _ = ports.append(dd1.port) %}
            {%     endif %}
            {%   endfor %}
            {% endfor %}{{ ports }}"
      vars:
        domain_definition:
          - name: server11
            cluster: cluster1
            db_servers:
              - server12
              - server21
            port: '8080'
          - name: server12
            cluster: cluster1
            db_servers:
              - server22
            port: '8090'
          - name: server13
            cluster: cluster1
            port: '8091'
          - name: server21
            cluster: cluster2
            db_servers:
              - server12
              - server22
            port: '9080'
          - name: server22
            cluster: cluster2
            port: '9090'

    - name: Show the extracted ports
      debug:
        msg: "{{ db_used_ports }}"

jean-christophe manciot

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Feb 7, 2022, 3:52:47 AM2/7/22

to Ansible Project

Thanks, your first answer is exactly what I was looking for. :-)

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