MQTT Commands

MQTT Control driver offers several commands to interact with an MQTT device.

Overview

Following commands are available

Command	Description	Details
mqtt:writedata	publish data to a topic	[Write Data]
mqtt:readdata	try to receive data from a topic	[Read Data]
mqtt:exchangedata	exchange data with a send-topic and a receive-topic	[Exchange Data]

Address Variables

Each Address (MQTT Topic) argument supports resolving variables. All device properties are resolved as variables. See Address Variables

Command node Properties

Each command node can have the following properties

Name	Description	DataType	Necessity
Retain	Sends the values with the retain flag to the broker	System.Boolean	Optional
ContentType	Special property for payload processing. See Payload Extractor	System.String	Optional
Mapping:Value	Special property for payload processing. See Payload Extractor	System.String	Optional

Write Data

This command allows to publish data to a specific MQTT topic. The command address is mqtt:writedata.

Input arguments

Name	Description	DataType	Necessity
Address	MQTT Topic to publish	System.String	Mandatory
Value	Value to publish	System.String	Mandatory
DataType	Optional value type for correct converting	System.String	Optional

The write data command has no output arguments.

Configuration example

{
  "Id": "77f3d77f-a20e-4550-9866-44ba24b8e14a",
  "Name": "WriteData",
  "Address": "mqtt:writedata",
  "ScriptFile": "",
  "Type": "CommandNode",
  "Arguments": [
    {
      "Name": "Address",
      "DataType": "System.String",
      "Description": "MQTT Topic"
    },
    {
      "Name": "Value",
      "DataType": "System.String",
      "Description": "Value as string"
    },
    {
      "Name": "DataType",
      "DataType": "System.String",
      "Description": "Optional: DataType"
    }
  ],
  "Properties": [
    {
      "Name": "ContentType",
      "DataType": "System.String",
      "Value": "UTF8.JSON"
    },
    {
      "Name": "Mapping:Value",
      "DataType": "System.String",
      "Value": "test"
    },
    {
      "Name": "Retain",
      "DataType": "System.Boolean",
      "Value": "true"
    }
  ]
}

Read Data

This command waits for a message from the broker under a specific MQTT topic. The command address is mqtt:readdata.

Input arguments

Name	Description	DataType	Necessity
Address	MQTT Topic to publish	System.String	Mandatory
DataType	Optional value type for correct converting	System.String	Optional

Output arguments

Name	Description	DataType	Necessity
Value	Value to publish	System.String	Mandatory

Configuration example

{
  "Id": "8dfdace7-e8a8-464b-9839-6fe1330d39a6",
  "Name": "ReadData",
  "Address": "mqtt:readdata",
  "ScriptFile": "",
  "Type": "CommandNode",
  "Arguments": [
    {
      "Name": "Address",
      "DataType": "System.String",
      "Description": "MQTT Topic"
    },
    {
      "Name": "Value",
      "Type": "Output",
      "DataType": "System.String",
      "Description": "Value as string"
    }
  ],
  "Properties": [
    {
      "Name": "ContentType",
      "DataType": "System.String",
      "Value": "UTF8.JSON"
    },
    {
      "Name": "Mapping:Value",
      "DataType": "System.String",
      "Value": "val"
    },
    {
      "Name": "Retain",
      "DataType": "System.Boolean",
      "Value": "true"
    }
  ]
}

Exchange Data

This command sends a message to the broker under the Request MQTT topic. The command then waits for a response from a response topic. Command address is mqtt:exchangedata.

Input arguments

Name	Description	DataType	Necessity
RequestAddress	MQTT Topic to publish	System.String	Mandatory
ResponseAddress	MQTT Topic to receive	System.String	Mandatory
RequestValue	Value to publish	System.String	Mandatory
DataType	Optional value type for correct converting	System.String	Optional

Output arguments

Name	Description	DataType	Necessity
ResponseValue	Value to publish	System.String	Mandatory

Configuration example

{
  "Id": "bfefe882-efb7-4759-84f8-1757f95bf6fa",
  "Name": "ExchangeData",
  "Address": "mqtt:exchangedata",
  "ScriptFile": "",
  "Type": "CommandNode",
  "Arguments": [
    {
      "Name": "RequestAddress",
      "DataType": "System.String",
      "Description": "MQTT request topic"
    },
    {
      "Name": "ResponseAddress",
      "DataType": "System.String",
      "Description": "MQTT response topic"
    },
    {
      "Name": "RequestValue",
      "DataType": "System.String",
      "Description": "Value to send"
    },
    {
      "Name": "DataType",
      "DataType": "System.String",
      "Description": "Optional: Data type of exchanged value"
    },
    {
      "Name": "ResponseValue",
      "Type": "Output",
      "DataType": "System.String",
      "Description": "Received value"
    }
  ],
  "Properties": []
}