QuickOPC User's Guide and Reference
MqttJson Field
Example 



OpcLabs.EasyOpcUA Assembly > OpcLabs.EasyOpc.UA.PubSub.Engine Namespace > UAPubSubTransportProfileUriStrings Class : MqttJson Field
Transport profile URI string for OPC UA PubSub over Message Queue Telemetry Transport (MQTT) with JSON message mapping.
Syntax
'Declaration
 
Public Const MqttJson As String
'Usage
 
Dim value As String
 
value = UAPubSubTransportProfileUriStrings.MqttJson
public const string MqttJson
public:
const String^ MqttJson
Example

.NET

COM

// This example shows how to subscribe to all dataset messages on an OPC-UA PubSub connection with MQTT JSON mapping using
// TCP.
//
// The following package needs to be referenced in your project (or otherwise made available) for the MQTT transport to 
// work.
// - OpcLabs.MqttNet
// Refer to the documentation for more information.

using System;
using System.Collections.Generic;
using System.Threading;
using OpcLabs.EasyOpc.UA.PubSub;
using OpcLabs.EasyOpc.UA.PubSub.Engine;
using OpcLabs.EasyOpc.UA.PubSub.OperationModel;

namespace UADocExamples.PubSub._EasyUASubscriber
{
    partial class SubscribeDataSet
    {
        public static void MqttJsonTcp()
        {
            // Define the PubSub connection we will work with. Uses implicit conversion from a string.
            // Default port with MQTT is 1883.
            UAPubSubConnectionDescriptor pubSubConnectionDescriptor = "mqtt://opcua-pubsub.demo-this.com";
            // Specify the transport protocol mapping.
            // The statement below isn't actually necessary, due to automatic message mapping recognition feature; see
            // https://kb.opclabs.com/OPC_UA_PubSub_Automatic_Message_Mapping_Recognition for more details.
            pubSubConnectionDescriptor.TransportProfileUriString = UAPubSubTransportProfileUriStrings.MqttJson;

            // Define the arguments for subscribing to the dataset, specifying the MQTT topic name.
            var subscribeDataSetArguments = new UASubscribeDataSetArguments(pubSubConnectionDescriptor)
            {
                DataSetSubscriptionDescriptor = {CommunicationParameters = {BrokerDataSetReaderTransportParameters =
                {
                    QueueName = "opcuademo/json"
                }}}
            };

            // Instantiate the subscriber object and hook events.
            var subscriber = new EasyUASubscriber();
            subscriber.DataSetMessage += subscriber_DataSetMessage_MqttJsonTcp;

            Console.WriteLine("Subscribing...");
            subscriber.SubscribeDataSet(subscribeDataSetArguments);

            Console.WriteLine("Processing dataset message events for 20 seconds...");
            Thread.Sleep(20 * 1000);

            Console.WriteLine("Unsubscribing...");
            subscriber.UnsubscribeAllDataSets();

            Console.WriteLine("Waiting for 1 second...");
            // Unsubscribe operation is asynchronous, messages may still come for a short while.
            Thread.Sleep(1 * 1000);

            Console.WriteLine("Finished.");
        }

        static void subscriber_DataSetMessage_MqttJsonTcp(object sender, EasyUADataSetMessageEventArgs e)
        {
            // Display the dataset.
            if (e.Succeeded)
            {
                // An event with null DataSetData just indicates a successful connection.
                if (!(e.DataSetData is null))
                {
                    Console.WriteLine();
                    Console.WriteLine($"Dataset data: {e.DataSetData}");
                    foreach (KeyValuePair<string, UADataSetFieldData> pair in e.DataSetData.FieldDataDictionary)
                        Console.WriteLine(pair);
                }
            }
            else
            {
                Console.WriteLine();
                Console.WriteLine($"*** Failure: {e.ErrorMessage}");
            }
        }

        // Example output:
        //
        //Subscribing...
        //Processing dataset message events for 20 seconds...
        //
        //Dataset data: 2020-01-21T17:07:19.778,836,700,00; Good; Data; publisher=[String]31, class=eae79794-1af7-4f96-8401-4096cd1d8908, fields: 4
        //[BoolToggle, True {System.Boolean} @2020-01-21T16:07:19.778,836,700,00; Good]
        //[Int32, 482 {System.Int64} @2020-01-21T16:07:19.778,836,700,00; Good]
        //[Int32Fast, 2287 {System.Int64} @2020-01-21T16:07:19.778,836,700,00; Good]
        //[DateTime, 1/21/2020 5:07:19 PM {System.DateTime} @2020-01-21T16:07:19.778,836,700,00; Good]
        //
        //Dataset data: Good; Data; publisher=[String]32, fields: 4
        //[BoolToggle, True {System.Boolean}; Good]
        //[Int32, 482 {System.Int32}; Good]
        //[Int32Fast, 2287 {System.Int32}; Good]
        //[DateTime, 1/21/2020 5:07:19 PM {System.DateTime}; Good]
        //
        //Dataset data: Good; Data; publisher=[String]32, fields: 100
        //[Mass_0, 82 {System.Int64}; Good]
        //[Mass_1, 182 {System.Int64}; Good]
        //[Mass_2, 282 {System.Int64}; Good]
        //[Mass_3, 382 {System.Int64}; Good]
        //[Mass_4, 482 {System.Int64}; Good]
        //[Mass_5, 582 {System.Int64}; Good]
        //[Mass_6, 682 {System.Int64}; Good]
        //[Mass_7, 782 {System.Int64}; Good]
        //[Mass_8, 882 {System.Int64}; Good]
        //[Mass_9, 982 {System.Int64}; Good]
        //[Mass_10, 1082 {System.Int64}; Good]
        ////...
    }
}
# This example shows how to subscribe to all dataset messages on an OPC-UA PubSub connection with MQTT JSON mapping using
# TCP.
#
# The following package needs to be referenced in your project (or otherwise made available) for the MQTT transport to
# work.
# - OpcLabs.MqttNet
# Refer to the documentation for more information.

# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import opclabs_mqttnet
import time

# Import .NET namespaces.
from OpcLabs.EasyOpc.UA.PubSub import *
from OpcLabs.EasyOpc.UA.PubSub.Engine import *
from OpcLabs.EasyOpc.UA.PubSub.OperationModel import *


def dataSetMessage(sender, e):
    # Display the dataset.
    if e.Succeeded:
        # An event with null DataSetData just indicates a successful connection.
        if e.DataSetData is not None:
            print('')
            print('Dataset data: ', e.DataSetData, sep='')
            for pair in e.DataSetData.FieldDataDictionary:
                print(pair)
    else:
        print('')
        print('*** Failure: ', e.ErrorMessageBrief, sep='')
        print('*** Failure: ', e.Exception, sep='')


# Define the PubSub connection we will work with. Uses implicit conversion from a string.
# Default port with MQTT is 1883.
pubSubConnectionDescriptor = UAPubSubConnectionDescriptor.op_Implicit('mqtt://opcua-pubsub.demo-this.com')
# Specify the transport protocol mapping.
# The statement below isn't actually necessary, due to automatic message mapping recognition feature; see
# https://kb.opclabs.com/OPC_UA_PubSub_Automatic_Message_Mapping_Recognition for more details.
pubSubConnectionDescriptor.TransportProfileUriString = UAPubSubTransportProfileUriStrings.MqttJson

# Define the arguments for subscribing to the dataset, specifying the MQTT topic name.
subscribeDataSetArguments = UASubscribeDataSetArguments(pubSubConnectionDescriptor)
subscribeDataSetArguments.DataSetSubscriptionDescriptor.CommunicationParameters.BrokerDataSetReaderTransportParameters.\
    QueueName = 'opcuademo/json'

# Instantiate the subscriber object and hook events.
subscriber = EasyUASubscriber()
subscriber.DataSetMessage += dataSetMessage

print('Subscribing...')
IEasyUASubscriberExtension.SubscribeDataSet(subscriber, subscribeDataSetArguments)

print('Processing dataset message events for 20 seconds...')
time.sleep(20)

print('Unsubscribing...')
subscriber.UnsubscribeAllDataSets()

print('Waiting for 1 second...')
# Unsubscribe operation is asynchronous, messages may still come for a short while.
time.sleep(1)

subscriber.DataSetMessage -= dataSetMessage

print('Finished.')
Rem The following package needs to be referenced in your project (or otherwise made available) for the MQTT transport to 
Rem work.
Rem - OpcLabs.MqttNet
Rem Refer to the documentation for more information.

' The subscriber object, with events
'Public WithEvents Subscriber4 As EasyUASubscriber

Private Sub EasyUASubscriber_SubscribeDataSet_MqttJsonTcp_Command_Click()
    OutputText = ""
    
    ' Define the PubSub connection we will work with. Uses implicit conversion from a string.
    ' Default port with MQTT is 1883.
    Dim subscribeDataSetArguments As New EasyUASubscribeDataSetArguments
    Dim pubSubConnectionDescriptor As UAPubSubConnectionDescriptor
    Set pubSubConnectionDescriptor = subscribeDataSetArguments.dataSetSubscriptionDescriptor.ConnectionDescriptor
    pubSubConnectionDescriptor.ResourceAddress.ResourceDescriptor.UrlString = "mqtt://opcua-pubsub.demo-this.com:1883"
    ' Specify the transport protocol mapping.
    ' The statement below isn't actually necessary, due to automatic message mapping recognition feature; see
    ' https://kb.opclabs.com/OPC_UA_PubSub_Automatic_Message_Mapping_Recognition for more details.
    pubSubConnectionDescriptor.TransportProfileUriString = "http://opcfoundation.org/UA-Profile/Transport/pubsub-mqtt-json" ' UAPubSubTransportProfileUriStrings.MqttJson

    ' Define the arguments for subscribing to the dataset, specifying the MQTT topic name.
    subscribeDataSetArguments.dataSetSubscriptionDescriptor.CommunicationParameters.BrokerDataSetReaderTransportParameters.QueueName = "opcuademo/json"
    
    ' Instantiate the subscriber object and hook events.
    Set Subscriber4 = New EasyUASubscriber
    
    OutputText = OutputText & "Subscribing..." & vbCrLf
    Call Subscriber4.SubscribeDataSet(subscribeDataSetArguments)

    OutputText = OutputText & "Processing dataset message for 20 seconds..." & vbCrLf
    Pause 20000

    OutputText = OutputText & "Unsubscribing..." & vbCrLf
    Subscriber4.UnsubscribeAllDataSets

    OutputText = OutputText & "Waiting for 1 second..." & vbCrLf
    ' Unsubscribe operation is asynchronous, messages may still come for a short while.
    Pause 1000

    Set Subscriber1 = Nothing

    OutputText = OutputText & "Finished." & vbCrLf
End Sub

Private Sub Subscriber4_DataSetMessage(ByVal sender As Variant, ByVal eventArgs As EasyUADataSetMessageEventArgs)
    ' Display the dataset
    If eventArgs.Succeeded Then
        ' An event with null DataSetData just indicates a successful connection.
        If Not eventArgs.DataSetData Is Nothing Then
            OutputText = OutputText & vbCrLf
            OutputText = OutputText & "Dataset data: " & eventArgs.DataSetData & vbCrLf
            Dim dictionaryEntry2: For Each dictionaryEntry2 In eventArgs.DataSetData.FieldDataDictionary
                OutputText = OutputText & dictionaryEntry2 & vbCrLf
            Next
        End If
    Else
        OutputText = OutputText & vbCrLf
        OutputText = OutputText & eventArgs.ErrorMessageBrief & vbCrLf
    End If
End Sub
' Example output:
'
'Subscribing...
'Processing dataset message events for 20 seconds...
'
'Dataset data: 2020-01-21T17:07:19.778,836,700,00; Good; Data; publisher=[String]31, class=eae79794-1af7-4f96-8401-4096cd1d8908, fields: 4
'[BoolToggle, True {System.Boolean} @2020-01-21T16:07:19.778,836,700,00; Good]
'[Int32, 482 {System.Int64} @2020-01-21T16:07:19.778,836,700,00; Good]
'[Int32Fast, 2287 {System.Int64} @2020-01-21T16:07:19.778,836,700,00; Good]
'[DateTime, 1/21/2020 5:07:19 PM {System.DateTime} @2020-01-21T16:07:19.778,836,700,00; Good]
'
'Dataset data: Good; Data; publisher=[String]32, fields: 4
'[BoolToggle, True {System.Boolean}; Good]
'[Int32, 482 {System.Int32}; Good]
'[Int32Fast, 2287 {System.Int32}; Good]
'[DateTime, 1/21/2020 5:07:19 PM {System.DateTime}; Good]
'
'Dataset data: Good; Data; publisher=[String]32, fields: 100
'[Mass_0, 82 {System.Int64}; Good]
'[Mass_1, 182 {System.Int64}; Good]
'[Mass_2, 282 {System.Int64}; Good]
'[Mass_3, 382 {System.Int64}; Good]
'[Mass_4, 482 {System.Int64}; Good]
'[Mass_5, 582 {System.Int64}; Good]
'[Mass_6, 682 {System.Int64}; Good]
'[Mass_7, 782 {System.Int64}; Good]
'[Mass_8, 882 {System.Int64}; Good]
'[Mass_9, 982 {System.Int64}; Good]
'[Mass_10, 1082 {System.Int64}; Good]
'...
Remarks

Profile author: OPC Foundation

Requirements

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2016, Windows Server 2022; .NET: Linux, macOS, Microsoft Windows

See Also