class QOpcUaGenericStructHandler#

Reads a server’s data types and decodes/encodes generic structs from/to extension objects. More…

New in version 6.7.

Synopsis#

Methods#

def __init__()
def addCustomEnumDefinition()
def dataTypeKindForTypeId()
def enumDefinitionForTypeId()
def initialize()
def isAbstractTypeId()
def typeIdForBinaryEncodingId()
def typeNameForBinaryEncodingId()
def typeNameForTypeId()

Signals#

def initializeFinished()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description#

The binary data encoding used in OPC UA was designed with a small message size in mind and doesn’t contain any information about the structure of the data. This means that a decoder must known the structure of the encoded data in advance to be able to decode a data buffer.

Since OPC UA 1.04, nodes of the DataType node class may have the DataTypeDefinition attribute which contain information about the fields of structured types and the mapping of enum values to names. Together with the knowledge about how to decode built-in types, this allows a client to decode generic custom structured types without relying on outside knowledge.

QOpcUaGenericStructHandler traverses the type hierarchy of a server by following the HasSubtype references starting from BaseDataType and reads the DataTypeDefinition attribute of the nodes.

For structured types where a QOpcUaStructureDefinition value is present in the DataTypeDefinition attribute, automatic decoding of extension objects containing them is available. Fields with a built-in type or a type where a C++ data class exists are deserialized to the corresponding Qt OPC UA type, other generic structs are serialized to a nested QOpcUaGenericStructValue . All nested generic struct values must have a QOpcUaStructureDefinition in the server or decoding fails.

The same conditions apply to encoding a custom struct.

Example for decoding a custom struct:

QOpcUaGenericStructHandler handler(opcuaClient);
handler.initialize();

QObject::connect(&handler, &QOpcUaGenericStructHandler::initializeFinished, [opcuaClient, &handler](bool success) {
    if (!success)
        return;

    auto node = opcuaClient->node("ns=4;i=3003"); // A custom struct test node in the open62541-testserver
    node->readValueAttribute();

    QObject::connect(node, &QOpcUaNode::attributeRead, [node, &handler](QOpcUa::NodeAttributes attr) {
        if (!attr.testFlag(QOpcUa::NodeAttribute::Value) || node->valueAttributeError() != QOpcUa::UaStatusCode::Good)
            return;

        auto extObj = node->valueAttribute().value<QOpcUaExtensionObject>();
        qDebug() << "Got object of type" << handler.typeNameForBinaryEncodingId(extObj.encodingTypeId());

        const auto result = handler.decode(extObj);

        if (!result)
            return;

        qDebug() << *result;
    });
});

Example for encoding a custom struct:

QOpcUaGenericStructHandler handler(opcuaClient);
handler.initialize();

QObject::connect(&handler, &QOpcUaGenericStructHandler::initializeFinished, [opcuaClient, &handler](bool success) {
    if (!success)
        return;

    QOpcUaGenericStructValue value = handler.createGenericStructValueForTypeId("ns=4;i=3006");
    value.fieldsRef()["MandatoryMember"] = 23.0;
    value.fieldsRef()["OptionalMember"] = 42.0;

    const auto ext = handler.encode(value);

    if (!ext)
        return;

    // Use the extension object to write a node's value attribute, in a method parameter, etc...
});

class DataTypeKind#

This enum type specifies data type kind of a data type node.

Constant

Description

QOpcUaGenericStructHandler.DataTypeKind.Unknown

The type node id is unknown.

QOpcUaGenericStructHandler.DataTypeKind.Struct

The type node id belongs to a structured type.

QOpcUaGenericStructHandler.DataTypeKind.Enum

The type node id belongs to an enum type.

QOpcUaGenericStructHandler.DataTypeKind.Other

The type node id belongs to a type which is not a struct or enum (other built-in types or their subtypes)

Constant	Description
QOpcUaGenericStructHandler.DataTypeKind.Unknown	The type node id is unknown.
QOpcUaGenericStructHandler.DataTypeKind.Struct	The type node id belongs to a structured type.
QOpcUaGenericStructHandler.DataTypeKind.Enum	The type node id belongs to an enum type.
QOpcUaGenericStructHandler.DataTypeKind.Other	The type node id belongs to a type which is not a struct or enum (other built-in types or their subtypes)

__init__(client[, parent=None])#

Parameters:

client – QOpcUaClient
parent – QObject

Constructs a generic struct handler for client.

addCustomEnumDefinition(definition, typeId, name[, isAbstract=false])#

Parameters:

definition – QOpcUaEnumDefinition
typeId – str
name – str
isAbstract – bool

Return type:

bool

Adds the custom enum definition definition to the known types. This can be used to support custom structures the server doesn’t expose a StructureDefinition for. The parameters definition, typeId and name are required for proper decoding and encoding. If isAbstract is set, the type can’t be encoded and decoded.

Returns true if the enum definition was successfully added.

dataTypeKindForTypeId(id)#

Parameters:: id – str
Return type:: DataTypeKind

Returns the data type kind for the type node id id.

enumDefinitionForTypeId(id)#

Parameters:: id – str
Return type:: QOpcUaEnumDefinition

Returns the QOpcUaEnumDefinition for the type node id id. If the node id is unknown or does not belong to an enum type, a default constructed value is returned.

initialize()#

Return type:: bool

Starts the data type hierarchy traversal. Success or failure is reported in the initializeFinished signal.

Returns false if the operation can’t be started.

initializeFinished(success)#

Parameters:: success – bool

This signal is emitted when the initialization has finished. success indicates if the initialization was successful.

isAbstractTypeId(id)#

Parameters:: id – str
Return type:: bool

Returns true if the data type described by id is abstract.

typeIdForBinaryEncodingId(id)#

Parameters:: id – str
Return type:: str

Returns the type node id associated with the binary encoding id id.

typeNameForBinaryEncodingId(id)#

Parameters:: id – str
Return type:: str

Returns the type name belonging to the binary encoding node id id. If the node id is unknown or does not belong to a struct type, an empty string is returned.

typeNameForTypeId(id)#

Parameters:: id – str
Return type:: str

Returns the type name belonging to a data type node identified by type node id id. If the node id is unknown, an empty string is returned.