How to fix Invalid Data Error in Azure Stream Analytics?

Question

I am trying to create a stream analytics job from my IoT Hub to Power BI but my Input data seams to be invalid. After starting the Job I get this Error Code: InputDeserializerError.InvalidData . My Event serialization format is JSON. I monitored my messages via the azure shell and they look like this:

    "event": {
        "origin": "Projektpi",
        "module": "",
        "interface": "",
        "component": "",
        "payload": "{\"Time\": 19/04/2021, 13:22:33, \"Critical vibration\": No, \"Temperature\": 20.812, \"RPM\": 0.0}"
    }

Every 11 seconds I send messages from my pi via this code:

client = IoTHubDeviceClient.create_from_connection_string(CONNECTION_STRING)

async def send_to_azure(payload):

    # await internet connection
    awaitConnection()
    # payload looks like this: payload = '{{"Time": {now}, "Critical vibration": {azurevibration}, "Temperature": {azuretemp}, "RPM": {azurerpm}}}'
    message = Message(payload)

    # Send a message to the IoT hub
    print(f"Sending message: {message}")
    try:
         print('Status: Trying to send data to Azure IoT Hub...')
         await client.connect()
         await client.send_message(message)
         print('Status: Data sent ...')
    except:
         print('Status: Problem sending data to Azure IoT Hub...') 

How do I have to change my code so that the Stream Analytics Job can use my pi sensor data as Input? If you know of a python tutorial etc. that would be great. I am quite new to azure and programming in general so thank you very much for your help!

Answer 1

Your payload contains some invalid JSON. Stream Analytics will try to deserialize your JSON payload and run into an error. The faulty payload is caused by two properties:

• "Time"
• "Critical vibration"

Both are missing double quotes around the value, these are needed for text fields, not for numerical fields. This should be the correct format:

"event": {
        "origin": "Projektpi",
        "module": "",
        "interface": "",
        "component": "",
        "payload": "{\"Time\": \"19/04/2021, 13:22:33\", \"Critical vibration\": \"No\", \"Temperature\": 20.812, \"RPM\": 0.0}"
    }

For clarity, I'll include the unescaped version of your payload:

{
   "Time":"19/04/2021, 13:22:33",
   "Critical vibration":"No",
   "Temperature":20.812,
   "RPM":0.0
}