Assign Ansible variable to dynamic array of JSON objects using Jinja2 template

Question

I have an Ansible variable called port_mapping that is assigned an array of JSON objects. I want to create this array of JSON objects in a dynamic way using Jinja2 templates.

    ports_mapping:
        - name: Et1
          port_number: 1
          type: access
          vlan: 1
        - name: Et2
          port_number: 2
          type: access
          vlan: 1
        - name: Et3
          port_number: 3
          type: access
          vlan: 1
        - name: Et4
          port_number: 4
          type: access
          vlan: 1

Here's what I am trying to do and it's throwing errors, I think it's reading the spacing wrong so it doesn't interpret it as an array of json objects. In this example, I want to create 30 JSON objects.

ports_mapping: "{{ lookup('template', 'switchports.j2') }}"

switchports.j2

{% for i in range(1,30) %}
- name: Et{{ i }}
  port_number: {{ i }}
  type: access
  vlan: 1
{% endfor %}

Can someone please recommend how I can achieve what I am trying to do?

Answer 1

The result of the template is string

    - debug:
        var: ports_mapping
    - debug:
        var: ports_mapping|type_debug

give (the range limited to 2 items)

  ports_mapping: |-
    - name: Et1
      port_number: 1
      type: access
      vlan: 1
    - name: Et2
      port_number: 2
      type: access
      vlan: 1

  ports_mapping|type_debug: str

Use the filter from_yaml to convert the string to the list

ports_mapping: "{{ lookup('template', 'switchports.j2')|from_yaml }}"

Then the tasks above give

  ports_mapping:
  - name: Et1
    port_number: 1
    type: access
    vlan: 1
  - name: Et2
    port_number: 2
    type: access
    vlan: 1

  ports_mapping|type_debug: list