SOLVED: Using template to parse JSON from MQTT

Configuration
1

Hi there,

I’m now trying for hours to get that up and running and now complete lost any idea.

Here is the problem:

I’m sending via MQTT the following JSON payload:
{ "id": "01", "name": "WeatherStation", "sensors": [ { "id": "01", "type": "HUD21", "temperature": 26.09, "airPressure": 101573.00, "humidity": 12.09, "lightLevel": 45145.0, "batteryCharge": 12.09, "batteryVoltage": 12.12 }, { "id": "02", "type": "DHT21", "temperature": 26.09, "humidity": 56.73, "heatIndex": 34.22, "dewPointDHT": 34.22 } ] }

The message arrives in HA and I receive a number of error messages, that “Error parsing value: ‘value_json’ is undefined”.

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However, if I use the template test configurator everything works fine. See picture below.

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I tested various ideas in my configuration.yaml but nothing seems to work.
Here three different ideas:

  • platform: mqtt
    name: “WeatherStation - Humidity - DHT”
    state_topic: “WeatherStation/data”
    unit_of_measurement: ‘%’
    value_template: ‘{{ value_json.sensors.1.humidity }}’

  • platform: mqtt
    name: “WeatherStation - Humidity - DHT”
    state_topic: “WeatherStation/data”
    unit_of_measurement: ‘%’
    value_template: ‘{{ states.sensors.1.humidity }}’

  • platform: mqtt
    name: “WeatherStation - HeatIndex - DHT”
    state_topic: “WeatherStation/data”
    unit_of_measurement: ‘HI’
    value_template: ‘{{ states.sensor.sensors.1.heatIndex }}’

  • platform: mqtt
    name: “WeatherStation - Dew Point - DHT”
    state_topic: “WeatherStation/data”
    unit_of_measurement: ‘°C’
    value_template: “{{ value_json.state }}”
    payload_available: “online”
    payload_not_available: “offline”
    json_template_attributes:
    id: “{{ state.sensor.sensors.0.temperature }}”

Thanks for any hint!
Cheers
Stefan

2

Try this {{ value_json.sensors[0].humidity }}

3

It brings the same error: “Error parsing value: ‘value_json’ is undefined”.

Do I have to define value_json anywhere or register it for MQTT JSON? When I use the template tester the first line is “Imitate available variables: {% set value_json = …” then I test my template again “value_json”. But how is it defined without using the template tester.

Even with the simplest JSON it is not working (no nesting JSON). It is strange.

4

It is defined automatically within the the bowels of HA. You don’t have to do anything except refer to it in your value_template. I believe the full example should be

  platform: mqtt
  name: “WeatherStation - Humidity - DHT”
  state_topic: “WeatherStation/data”
  unit_of_measurement: ‘%’
  value_template: {{ value_json.sensors[0].humidity }}

Try removing all the other references to this topic - they may be causing the error inadvertently.

Also, the name may cause problems in the future. Try to keep the name to simple lower case ascii.

5

Thank you very much gpbenton for your guidance. It works now, as you proposed. Seems like using several variants in the config file crashed the “value_json”. Even the naming with “-” seems like problematic.

Thanks

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