Sometimes it’s necessary to do complex data translation or to have function-kind of logic. To allow such things, go-home provides mappers. Mappers are set of functions which could be applied for data-transformation.

Mappers are using govaluate library.

Supported functions

• num – converts value to number (float64 to be precise)
• str – converts value to string
• fmt – formats data using fmt.Sprintf
• jq – JSON operations

jq

If jq is invoked with an object only, function returns un-marshaled map[string]interface{} data.

If jq is invoked with object and expression, function tries to apply jq syntax and execute it over the object.

Read

Read mapper is passing received payload into mapper method and expects to receive single object.

For example, you can map received MQTT payload into device state.

Write

Write mapper is passing invoking object into mapper method and expects to receive single object.

For example, you can use device state to map it into desired MQTT command.

Examples

The following expression will return true

jq(payload, '.status.value') == 'true'

with the following payload

{
  "status": {
    "value": true
  }
}

The following expression will return on:

(state.On == true) ? 'on' : 'off'

with the following device state:

LightState{
    On: true,
}

The following expression will return r:10,g:20,b:30:

fmt('r:%v,g:%v,b:%v', state.Color.R, state.Color.G, state.Color.B)

with the following device state:

LightState{
    On: true,
    Color: common.Color{
        R: 10,
        G: 20,
        B: 30,
    },
}