[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 😎