CODEWITHSUNDEEP
opcopc-ua
Muckers Mate
Muckers Mate

Reputation: 429

OPC UA How to read a datatype from the server

I can't seem to figure this one out:

Before writing to a tag I need to know what data type it is expecting(the value that mywrite function receives is always a string).

I realise you have to read the datatype from the server and here's my code to do so, but I'm at a loss as to how to use the information returned:

var nodesToRead = BuildReadValueIdCollection(node.DisplayName, Attributes.DataType);

                    DataValueCollection readResults;
                    DiagnosticInfoCollection diag;
                    _session.Read(
                        requestHeader: null,
                        maxAge: 0,
                        timestampsToReturn: TimestampsToReturn.Neither,
                        nodesToRead: nodesToRead,
                        results: out readResults,
                        diagnosticInfos: out diag);
                    var val = readResults[0];

What do I do with val to determine what the datatype is?

Do I use Val.Value or Val.WrappedValue or Val.WrappedValue.Value (whatever the difference is ?)

The tag I've been using to test has returned Val = "i=6".....

What is this referring to?

What datatype is "6" and

how do I convert val to something I can use.

Any help would be greatly appreciated.

Thanks

Upvotes: 4

Views: 8389

Answers (4)

Johannes Weih
Johannes Weih

Reputation: 171

We use this extension method to determine the C# type of nodes:

public static Type GetSystemType(this Session session, NodeId nodeId)
{
  var currentValue = session.ReadValue(nodeId);
  var builtInType = currentValue.WrappedValue.TypeInfo.BuiltInType;
  var valueRank = currentValue.WrappedValue.TypeInfo.ValueRank;

  return TypeInfo.GetSystemType(builtInType, valueRank);
}

It is somewhat a hack but it works well.

Upvotes: 1

Etienne
Etienne

Reputation: 16867

In recent version, node-opcua client has been extended with a utility function ClientSession#getBuiltInDataType that does this for you.

var nodeId = coerceNodeId("ns=411;s=Scalar_Simulation_Int64");
session.getBuiltInDataType(nodeId,function(err,dataType){
     if(!err){
       console.log("Use data Type",dataType," to write into UAVariable", nodeId.toString();
    }
});

Upvotes: 1

ZbynekZ
ZbynekZ

Reputation: 1608

Reading from the DataType attribute returns a NodeID of the OPC UA type. It can be one of the "standard" types defined in the OPC UA spec, or something specific to the server. The standard types reside in namespace 0, which is your case (as there is no "ns=..." part in the displayed Node ID), and "i=6" stands for Int32.

There are many types with pre-defined Node IDs, and you need to consult the OPC UA specs, or the nodeset files that come with the stacks/SDKs (e.g. Opc.Ua.NodeSet.xml), to figure out what they mean.

Upvotes: 6

Jouni Aro
Jouni Aro

Reputation: 2139

The value is a NodeId referring to the data type node. You can compare the value to known NodeId values (DataTypeIds in .NET or something, not sure about this right away) or you will need to find the data type node from the address space.

Upvotes: 1

Related Questions