OPCUA DataTypes

[H4rw3y5ag3]

Hi @GianfriAur ,

I have a question, this time about the dataTypes.
Maybe I'm looking into the wrong file (NodeId.php). But I was wondering if there are only the 4 datatypes "numeric", "string", "guid" and "opaque", if I query for example: $dataType = $node->reference->referenceTypeId->type
The OPCUA specification defines at least 25 buiuld in datatypes: https://reference.opcfoundation.org/specs/OPC-10000-6/5.1.2
I'm intersted in a solution to check in a general way the node datatypes. Example INT16, UINT16, INT32 and UINT32... I've found some datatypes in the documentation data-value-and-variant and expected that those are returned as a nodeDataType.

[H4rw3y5ag3]

Not sure if this is the most efficient way, but it seems to work:

// If it's a variable, we can also read its value's data type (if available) 
$valueDataType = $client->read($node->reference->nodeId)->getVariant()->type->name ?? null;

[GianfriAur]

Hi @H4rw3y5ag3

great question, and the confusion is totally understandable: two unrelated concepts share the word "type".

What you found

The four constants

public const TYPE_NUMERIC = 'numeric';
public const TYPE_STRING  = 'string';
public const TYPE_GUID    = 'guid';
public const TYPE_OPAQUE  = 'opaque';

live in src/Types/NodeId.php, not in BuiltinType.php. They identify how the NodeId itself is encoded ? its identifier
kind, matching the four OPC UA NodeId forms (i=?, s=?, g=?, b=?). See Types NodeId Factories.

The 25 built-in OPC UA data types

What you're actually looking for lives in src/Types/BuiltinType.php the enum that covers every OPC UA built-in type from Part
6:

case Boolean = 1;
case SByte = 2;   case Byte = 3;
case Int16 = 4;   case UInt16 = 5;
case Int32 = 6;   case UInt32 = 7;
case Int64 = 8;   case UInt64 = 9;
case Float = 10;  case Double = 11;
case String = 12; case DateTime = 13;
case Guid = 14;   case ByteString = 15;
case XmlElement = 16;
case NodeId = 17; case ExpandedNodeId = 18;
case StatusCode = 19;
case QualifiedName = 20; case LocalizedText = 21;
case ExtensionObject = 22;
case DataValue = 23; case Variant = 24;
case DiagnosticInfo = 25;

Your answer is exactly right

$type = $client->read($node->reference->nodeId)->getVariant()->type;
// returns a BuiltinType ? e.g. BuiltinType::Int32, BuiltinType::UInt16, 

That gives you the actual data type the server populated the variant with. The 4 NodeId selectors and the 25 BuiltinType cases never overlap, they answer two different questions:

You want to know?	Use?
How the NodeId string is shaped (numeric/string/GUID/opaque)	NodeId::$type (one of the four TYPE_* constants)
What data type the value has	$dv->getVariant()->type (a BuiltinType case)

Bonus read the DataType attribute without fetching the value

If you only need the type metadata (e.g. for variables you can't read, or to avoid the round-trip on a hot path), read the DataType attribute directly:

use PhpOpcua\Client\Types\AttributeId;

$dataTypeNodeId = $client->read($nodeId, AttributeId::DataType)->getValue();
// ? a NodeId of the DataType definition (e.g. i=6 = Int32, i=4 = Int16, ?)

The numeric IDs of the standard types match the BuiltinType enum values (Int32 = 6, UInt32 = 7, etc.). For custom Structure DataTypes you'd then call discoverDataTypes() once to get the schema decoded
automatically.

---

A possible API improvement worth considering: rename NodeId::$type in NodeId::$identifierType to remove exactly this ambiguity

in addition I will prepare in the v4.4.0 release also $type = $client->read($node->reference->nodeId)->getType() to directly access the result type

Does this seem like a possible improvement to the API?

[GianfriAur]

Hi @H4rw3y5ag3

I finally released 4.4.0, if you want to upgrade just do the backwards compatibility is 100%,
as anticipated the new API to easily access the type is

$dv = $client->read('ns=2;s=Devices/PLC/Speed');

$dv->getType(); // BuiltinType::Double
//or
$dv->type; // BuiltinType::Double

If you have any other questions, just ask

[H4rw3y5ag3]

Sorry for delay, Hey great work, thanks a lot. I really appreciate the new improvements of the API. 🥳