Problem with map when the key does not exist

Question

I have a var_file with this format:

bds_info:

  - id:   BD1
    db_name: BD1
    db_port: XXXX
    server: server1
    repo_url: repo1

  - id:   BD2
    db_name: BD2
    db_port: XXXX
    server: server2
    repo_url: repo2
    scan_name: scan2

What I'm trying to do is to select the scan_name from the var_file into a variable like this:

var_scan_name_to_use:       "{{ (bds_info   | selectattr('id', 'equalto', (db_name|upper) ) | map(attribute='scan_name') | join) }}"

it works correctly if the id selected has the key but if it hasn't then I get the following error:

{
    "msg": "The task includes an option with an undefined variable. The error was: 'dict object' has no attribute 'scan_name
}

Is it possible to return undefined instead of a lookup error?

Answer 1

You can specify a default value to use if an object in the list does not have the given attribute.

{{ users|map(attribute="username", default="Anonymous")|join(", ") }}

^{Source: https://jinja.palletsprojects.com/en/2.11.x/templates/#map}

---

So, given the task:

- debug:
    msg: >-
      {{
        bds_info
          | selectattr('id', 'equalto', db_name | upper)
          | map(attribute='scan_name', default='undefined')
          | join
      }}
  vars:
    db_name: BD1
    bds_info:
      - id: BD1
        db_name: BD1
        db_port: XXXX
        server: server1
        repo_url: repo1
      - id: BD2
        db_name: BD2
        db_port: XXXX
        server: server2
        repo_url: repo2
        scan_name: scan2

This yields:

ok: [localhost] => 
  msg: undefined