Usage Example of Struct needed, and check whether node exists and create if not

[Sayum24]

Hello.
I have 2 questions.

I'm working on the task to transfer dynamically sensor-data via opc ua.

These values are important which I receive from the machine with a sensorID:
value, timestamp, status_message, error

1. If the node with the name of the sensorID already exists the values should be transferred, if it doesn't exist then the node should be created.

2. I found the feature of new structs but I couldn't find out how to set the parameters of it.
   Here is the code I have till now.

Definition of struct

process_data_struct = await new_struct(server, idx, "ProcessDataStruct", [
    new_struct_field("Timestamp", ua.VariantType.DateTime, timestamp),
    new_struct_field("StatusMessage", ua.VariantType.String),
    new_struct_field("Error", ua.VariantType.Boolean),
    new_struct_field("CurrentValue", ua.VariantType.Float)
])

Check whether node is already exists if not create it. Is that about right to check whether the node already exists?

try:
    # check whether node is already created
    sensor_node_id = f"ns=2;s={sensorID}"  # find node
    sensor_node = await self.client.get_node(sensor_node_id)
except:
    # create new node
    newObject = await myobj.add_variable(idx, bname=sensorID, datatype=process_data_struct)

# TODO: put data into ´process_data_struct´

[Sayum24]

1. check whether node exists: there is a very helpfull stackoverflow answer:
   https://stackoverflow.com/a/78086111/11322034

2. about the struct I found a solution that works:

# defining struct (see 1. code in question post)
await server.load_data_type_definitions()  # very important to enable the struct idk
# create struct
dataScruct = ua.ProcessDataStruct()
# put mock/initial-data in struct
dataScruct.Timestamp = datetime.now()
dataScruct.CurrentValue = 55.5
dataScruct.Error = False
dataScruct.StatusMessage = ''
# add variable
sensor65 = await myobj.add_variable(idx, "Sensor65", ua.Variant(dataScruct, ua.VariantType.ExtensionObject))

# start server
async with server:
    self.logger.info("Server: server started!")
    while True:
        # putting actual data in the struct
        dataScruct = ua.ProcessDataStruct()
        dataScruct.Timestamp = datetime.strptime(timestamp, '%Y-%m-%d %H:%M:%S')
        dataScruct.CurrentValue = value
        dataScruct.Error = int(error)
        dataScruct.StatusMessage = status_message
        if sensorID == 65:
            await sensor65.set_value(dataScruct) # set data