[FR] Fallback value of a variable to another variable

[clau-bucur]

Describe the solution you'd like
Is it possible to define the default value of a variable, as the value of another variable?

Someting like:

my_template:
  default:
    - history_entity: '[[entity]]'
  card:
    type: my_card
    entity: '[[entity]]'
    tap_action:
      action: fire-dom-event
      browser_mod:
        service: browser_mod.more_info
        data:
          entity: '[[history_entity]]'

And when I call it withoiut specifying a value for history_entity it will use the value specified for the entity variable:

- type: custom:decluttering-card
  template: my_template
  variables:
    - entity: sensor.my_entity

[ildar170975]

Agree, a good idea, was thinking about same many times.

[droans]

Use a conditional card.

my_template:
  defaults:
    - history_entity: 'fake'
  card:
    type: vertical-stack
    cards:
      - type: conditional
        conditions:
          - condition: state
            entity: '[[ history_entity]]'
            state: "unavailable"
        card:
          - type: my_card
            entity: '[[entity]]'
            tap_action:
              action: fire-dom-event
              browser_mod:
                service: browser_mod.more_info
                data:
                  entity: '[[entity]]'
      - type: conditional
        conditions:
          - condition: state
            entity: '[[ history_entity]]'
            state_not: "unavailable"
        card:
          - type: my_card
            entity: '[[entity]]'
            tap_action:
              action: fire-dom-event
              browser_mod:
                service: browser_mod.more_info
                data:
                  entity: '[[history_entity]]'

A non-existent sensor will always return unavailable.

[ildar170975]

A non-existent sensor will always return unavailable.

I would say this is a bug in HA frontend because a non-existing entity's state is unknown.

[droans]

Woops, sorry. I meant unknown, not unavailable.

…

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[clau-bucur]

Use a conditional card.

my_template:
  defaults:
    - history_entity: 'fake'
  card:
    type: vertical-stack
    cards:
      - type: conditional
        conditions:
          - condition: state
            entity: '[[ history_entity]]'
            state: "unavailable"
        card:
          - type: my_card
            entity: '[[entity]]'
            tap_action:
              action: fire-dom-event
              browser_mod:
                service: browser_mod.more_info
                data:
                  entity: '[[entity]]'
      - type: conditional
        conditions:
          - condition: state
            entity: '[[ history_entity]]'
            state_not: "unavailable"
        card:
          - type: my_card
            entity: '[[entity]]'
            tap_action:
              action: fire-dom-event
              browser_mod:
                service: browser_mod.more_info
                data:
                  entity: '[[history_entity]]'

A non-existent sensor will always return unavailable.

Thanks for the suggestion, however that example is only a simple use-case where the request would be useful.

There are many more cases where the request comes handy.
Even in your example, the same end-result is much cleaner and easier achieved by using variable fallback.

[igorsantos07]

It is important to allow "templating" in the default values as well, so one could do as follows:

defaults:
  - entity: 'binary_sensor.[[area]]_presence'

This way, you could override the entity to be something else, or just go with the default based on the area name 😎

[Soukyuu]

what @igorsantos07 suggest is exactly what I'm missing, this could cut down my variable definitions considerably, still allowing to override the default for the variables that differ from it.

[droans]

Check out brunosabot/streamline-card. It's a fork of this card which has been maintained and has improved performance.

While it doesn't allow that specifically, you can use JavaScript templates in the card fields so you could do something like this:

entity_javascript: |
  if ('[[entity]]' == '') { 
    return DEFAULT_VALUE
  };
  return '[[entity]]';