QOpcUaNode#

QOpcUaNode allows interaction with an OPC UA node. More

Inheritance diagram of PySide6.QtOpcUa.QOpcUaNode

Synopsis#

Functions#

Signals#

Static functions#

Detailed Description#

The node is the basic building block of the OPC UA address space. It has attributes like browse name, value, associated properties and can have references to other nodes in the address space. Nodes are organized in namespaces and have IDs which can e.g. be numeric, a string, a namespace-specific format (opaque) or a globally unique identifier. A node is identified by the namespace ID and the node ID. This identifier is usually given as a string: The identifier of a node residing in namespace 0 and having the numeric identifier 42 results in the string ns=0;i=42. A node with a string identifier can be addressed via ns=0;s=myStringIdentifier.

Objects of this type are owned by the user and must be deleted when they are no longer needed. They are valid as long as the QOpcUaClient which created them exists.

Reading and writing of attributes#

The node attributes are read from the server when readAttributes() or readAttributeRange() is called. The results are cached locally and can be retrieved using attribute() after the attributeRead signal has been received.

Attributes can be written using writeAttribute() , writeAttributes() and writeAttributeRange() if the user has the necessary rights. Success of the write operation is reported using the attributeWritten signal.

attributeError() contains a status code associated with the last read or write operation on the attribute. This is the low level status code returned by the OPC UA service. This status code can be simplified by converting it to a ErrorCategory using errorCategory() .

Subscriptions and monitored items#

Subscriptions are a concept in OPC UA which allows receiving of notifications for changes in data or in case of events instead of continuously polling a node for changes. Monitored items define how attributes of a node are watched for changes. They are added to a subscription and any notifications they generate are forwarded to the user via the subscription. The interval of the updates as well as many other options of the monitored items and subscriptions can be configured by the user.

QOpcUaNode offers an abstraction to interact with subscriptions and monitored items. enableMonitoring() enables data change notifications for one or more attributes. The dataChangeOccurred signal contains new values and the local cache is updated. disableMonitoring() disables the data change notifications. The monitoringStatusChanged signal notifies about changes of the monitoring status, e. g. after manual enable and disable or a status change on the server.

Event monitoring uses the same API for setup and life cycle management. The EventNotifier attribute must be monitored using an EventFilter which selects the required event fields and filters the reported events by user defined criteria. The events are reported in the eventOccurred() signal as a QVariantList which contains the values of the selected event fields.

Settings of the subscription and monitored item can be modified at runtime using modifyMonitoring() .

Browsing the address space#

The OPC UA address space consists of nodes connected by references. browseChildren follows these references in forward direction and returns attributes from all nodes connected to the node behind an instance of QOpcUaNode in the browseFinished signal. browse() is similar to browseChildren() but offers more options to configure the browse call.

Method calls#

OPC UA specifies methods on the server which can be called by the user. QOpcUaNode supports this via callMethod which takes parameters and returns the results of the call in the methodCallFinished signal.

Resolving browse paths#

To support programming against a type description, OPC UA supports the resolution of a path of browse names starting from a certain node to obtain the node id of the target node. The resolveBrowsePath() method follows a path starting from the node it was called on and returns the result in the resolveBrowsePathFinished() signal.

Example#

For connecting the client to a server and getting a QOpcUaNode object, see QOpcUaClient .

After the node has been successfully created, the BrowseName of the root node is read from the server:

QOpcUaNode *rootNode; // Created before, see QOpcUaClient documentation.
// Connect to the attributeRead signal. Compatible slots of QObjects can be used instead of a lambda.
QObject::connect(rootNode, &QOpcUaNode::attributeRead, [rootNode, client](QOpcUa::NodeAttributes attr) {
    qDebug() << "Signal for attributes:" << attr;
    if (rootNode->attributeError(QOpcUa::NodeAttribute::BrowseName) != QOpcUa::UaStatusCode::Good) {
        qDebug() << "Failed to read attribute:" << rootNode->attributeError(QOpcUa::NodeAttribute::BrowseName);
        client->disconnectFromEndpoint();
    }
    qDebug() << "Browse name:" << rootNode->attribute(QOpcUa::NodeAttribute::BrowseName).value<QOpcUaQualifiedName>().name();
});
rootNode->readAttributes(QOpcUa::NodeAttribute::BrowseName); // Start a read operation for the node's BrowseName attribute.
class PySide6.QtOpcUa.QOpcUaNode#
static PySide6.QtOpcUa.QOpcUaNode.allBaseAttributes()#
Return type

NodeAttributes

Contains all attributes of the OPC UA base node class.

PySide6.QtOpcUa.QOpcUaNode.attribute(attribute)#
Parameters

attributeNodeAttribute

Return type

object

Returns the value of the attribute given in attribute.

The value is only valid after the attributeRead signal has been emitted. An empty QVariant is returned if there is no cached value for the attribute.

PySide6.QtOpcUa.QOpcUaNode.attributeError(attribute)#
Parameters

attributeNodeAttribute

Return type

UaStatusCode

Returns the error code for the attribute given in attribute.

The error code is only valid after the attributeRead or attributeWritten signal has been emitted.

If there is no entry in the attribute cache, BadNoEntryExists is returned.

See also

errorCategory

PySide6.QtOpcUa.QOpcUaNode.attributeRead(attributes)#
Parameters

attributesNodeAttributes

PySide6.QtOpcUa.QOpcUaNode.attributeUpdated(attr, value)#
Parameters
PySide6.QtOpcUa.QOpcUaNode.attributeWritten(attribute, statusCode)#
Parameters
PySide6.QtOpcUa.QOpcUaNode.browse(request)#
Parameters

requestPySide6.QtOpcUa.QOpcUaBrowseRequest

Return type

bool

Starts a browse call from this node.

Returns true if the asynchronous call has been successfully dispatched.

All references matching the criteria specified in request are returned in the browseFinished() signal.

For example, an inverse browse call can be used to find the parent node of a property node:

QOpcUaBrowseRequest request;
request.setBrowseDirection(QOpcUaBrowseRequest::BrowseDirection::Inverse);
request.setReferenceTypeId(QOpcUa::ReferenceTypeId::HasProperty);
propertyNode->browse(request);
PySide6.QtOpcUa.QOpcUaNode.browseChildren([referenceType=QOpcUa.ReferenceTypeId.HierarchicalReferences[, nodeClassMask=QOpcUa.NodeClass.Undefined]])#
Parameters
Return type

bool

Executes a forward browse call starting from the node this method is called on. The browse operation collects information about child nodes connected to the node and delivers the results in the browseFinished() signal.

Returns true if the asynchronous call has been successfully dispatched.

To request only children connected to the node by a certain type of reference, referenceType must be set to that reference type. For example, this can be used to get all properties of a node by passing HasProperty in referenceType. The results can be filtered to contain only nodes with certain node classes by setting them in nodeClassMask.

PySide6.QtOpcUa.QOpcUaNode.browseFinished(children, statusCode)#
Parameters
PySide6.QtOpcUa.QOpcUaNode.callMethod(methodNodeId[, args=list()])#
Parameters
  • methodNodeId – str

  • args

Return type

bool

Calls the OPC UA method methodNodeId with the parameters given via args. The result is returned in the methodCallFinished signal.

Returns true if the asynchronous call has been successfully dispatched.

PySide6.QtOpcUa.QOpcUaNode.client()#
Return type

PySide6.QtOpcUa.QOpcUaClient

Returns a pointer to the client that has created this node.

PySide6.QtOpcUa.QOpcUaNode.dataChangeOccurred(attr, value)#
Parameters
PySide6.QtOpcUa.QOpcUaNode.disableMonitoring(attr)#
Parameters

attrNodeAttributes

Return type

bool

This method disables monitoring for the attributes given in attr.

Returns true if the asynchronous call has been successfully dispatched.

After the call is finished, the disableMonitoringFinished signal is emitted and monitoringStatus returns a default constructed value with status code BadMonitoredItemIdIinvalid for attr.

PySide6.QtOpcUa.QOpcUaNode.disableMonitoringFinished(attr, statusCode)#
Parameters
PySide6.QtOpcUa.QOpcUaNode.enableMonitoring(attr, settings)#
Parameters
Return type

bool

This method creates a monitored item for each of the attributes given in attr. The settings from settings are used in the creation of the monitored items and the subscription.

Returns true if the asynchronous call has been successfully dispatched.

On completion of the call, the enableMonitoringFinished signal is emitted. There are multiple error cases in which a bad status code is generated: A subscription with the subscription id specified in settings does not exist, the node does not exist on the server, the node does not have the requested attribute or the maximum number of monitored items for the server is reached.

The same method is used to enable event monitoring. Events are special objects in the OPC UA address space which contain information about an event that has occurred. If an event is triggered on the server, an event monitored item collects selected values of node attributes of the event object and its child nodes. Every node that has an event source can be monitored for events. To monitor a node for events, the attribute EventNotifier must be monitored using an EventFilter which contains the event fields the user needs and optionally a where clause which is used to filter events by criteria (for more details, see EventFilter ).

PySide6.QtOpcUa.QOpcUaNode.enableMonitoringFinished(attr, statusCode)#
Parameters
PySide6.QtOpcUa.QOpcUaNode.eventOccurred(eventFields)#
Parameters

eventFields

static PySide6.QtOpcUa.QOpcUaNode.mandatoryBaseAttributes()#
Return type

NodeAttributes

Contains all mandatory attributes of the OPC UA base node class.

PySide6.QtOpcUa.QOpcUaNode.methodCallFinished(methodNodeId, result, statusCode)#
Parameters
  • methodNodeId – str

  • result – object

  • statusCodeUaStatusCode

PySide6.QtOpcUa.QOpcUaNode.modifyDataChangeFilter(attr, filter)#
Parameters
Return type

bool

Modifies an existing data change monitoring to use filter as data change filter.

Returns true if the filter modification request has been successfully dispatched to the backend.

monitoringStatusChanged for attr is emitted after the operation has finished.

PySide6.QtOpcUa.QOpcUaNode.modifyEventFilter(eventFilter)#
Parameters

eventFilterPySide6.QtOpcUa.QOpcUaMonitoringParameters.EventFilter

Return type

bool

Modifies an existing event monitoring to use eventFilter as event filter.

Returns true if the filter modification request has been successfully dispatched to the backend.

monitoringStatusChanged for EventNotifier is emitted after the operation has finished.

PySide6.QtOpcUa.QOpcUaNode.modifyMonitoring(attr, item, value)#
Parameters
Return type

bool

This method modifies settings of the monitored item or the subscription. The parameter item of the monitored item or subscription associated with attr is attempted to set to value.

Returns true if the asynchronous call has been successfully dispatched.

After the call has finished, the monitoringStatusChanged signal is emitted. This signal contains the modified parameters and the status code. A bad status code is generated if there is no monitored item associated with the requested attribute, modifying the requested parameter is not implemented or if the server has rejected the requested value.

PySide6.QtOpcUa.QOpcUaNode.monitoringStatus(attr)#
Parameters

attrNodeAttribute

Return type

PySide6.QtOpcUa.QOpcUaMonitoringParameters

Returns the monitoring parameters associated with the attribute attr. This can be used to check the success of enableMonitoring() or if parameters have been revised. The returned values are only valid after enableMonitoringFinished or monitoringStatusChanged have been emitted for attr. If the status is queried before a signal has been emitted, statusCode() returns BadNoEntryExists .

PySide6.QtOpcUa.QOpcUaNode.monitoringStatusChanged(attr, items, statusCode)#
Parameters
PySide6.QtOpcUa.QOpcUaNode.nodeId()#
Return type

str

Returns the ID of the OPC UA node.

PySide6.QtOpcUa.QOpcUaNode.readAttributeRange(attribute, indexRange)#
Parameters
Return type

bool

Starts an asynchronous read operation for the node attribute attribute. indexRange is a string which can be used to select a part of an array. It is defined in OPC-UA part 4, 7.22. The first element in an array is 0, “1” returns the second element, “0:9” returns the first 10 elements, “0,1” returns the second element of the first row in a two-dimensional array.

Returns true if the asynchronous call has been successfully dispatched.

Attribute values only contain valid information after the attributeRead signal has been emitted.

PySide6.QtOpcUa.QOpcUaNode.readAttributes([attributes=QOpcUaNode.mandatoryBaseAttributes()])#
Parameters

attributesNodeAttributes

Return type

bool

Starts an asynchronous read operation for the node attributes in attributes.

Returns true if the asynchronous call has been successfully dispatched.

Attribute values only contain valid information after the attributeRead signal has been emitted.

PySide6.QtOpcUa.QOpcUaNode.readHistoryRaw(startTime, endTime, numValues, returnBounds)#
Parameters
Return type

PySide6.QtOpcUa.QOpcUaHistoryReadResponse

Starts a read history request for this node. This is the Qt OPC UA representation for the OPC UA ReadHistory service for reading raw historical data defined in OPC-UA part 4, 5.10.3 . It reads the history based on the parementers, startTime, endTime, numValues, and returnBounds.

Returns a QOpcUaHistoryReadResponse which contains the state of the request if the asynchronous request has been successfully dispatched. The results are returned in the UaStatusCode serviceResult) signal.

In the following example, the historic data from the last two days of a node are requested and printed. The result is limited to ten values per node.

QOpcUaHistoryReadResponse *response = node->readHistoryRaw(QDateTime::currentDateTime(),
                                                           QDateTime::currentDateTime().addDays(-2),
                                                           10,
                                                           true);
if (response) {
    QObject::connect(response123, &QOpcUaHistoryReadResponse::readHistoryDataFinished,
                     [] (QList<QOpcUaHistoryData> results, QOpcUa::UaStatusCode serviceResult) {
        if (serviceResult != QOpcUa::UaStatusCode::Good) {
            qWarning() << "Fetching historical data failed with:" << serviceResult;
        } else {
            for (const auto& result : results) {
                qInfo() << "NodeId:" << result.nodeId();
                for (const auto &dataValue : result.result())
                    qInfo() << "Value:" << dataValue.value();
            }
        }
    });
}
PySide6.QtOpcUa.QOpcUaNode.readValueAttribute()#
Return type

bool

Starts an asynchronous read operation for the node’s Value attribute.

Returns true if the asynchronous call has been successfully dispatched.

See also

readAttributes()

PySide6.QtOpcUa.QOpcUaNode.resolveBrowsePath(path)#
Parameters

path

Return type

bool

Resolves the browse path path to one or more node ids starting from this node using the TranslateBrowsePathsToNodeIds service specified in OPC-UA part 4, 5.8.4.

Returns true if the asynchronous call has been successfully dispatched.

TranslateBrowsePathsToNodeIds is mainly used to program against type definitions instead of a concrete set of nodes in the OPC UA address space. For example, a type definition for a machine model could consist of a starting node with browse name “Machine” which has a component with browse name “Fan”. Fan has a component with browse name “RPM” which is a Variable node holding the current RPM value of the fan. There are multiple machines of that type and each of these machines is mapped into the OPC UA address space as an object of the machine type. For each of these machine objects, the path from the machine node to the “RPM” node is the same. If a client wants to read the current RPM value, it needs to call resolveBrowsePath() with the machine node as starting node and the browse path from the machine to the “RPM” node:

QScopedPointer<QOpcUaNode> node(opcuaClient->node("ns=1;s=machine1"));

QList<QOpcUaRelativePathElement> path;
path.append(QOpcUaRelativePathElement(QOpcUaQualifiedName(1, "Fan"), QOpcUa::ReferenceTypeId::HasComponent));
path.append(QOpcUaRelativePathElement(QOpcUaQualifiedName(1, "RPM"), QOpcUa::ReferenceTypeId::HasComponent));
node->resolveBrowsePath(path);

The result returned in resolveBrowsePathFinished() contains the node id of the “RPM” node which can be used to access the node’s attributes:

if (!results.size()) {
    qWarning() << "Browse path resolution failed";
    return;
}

if (results.at(0).isFullyResolved()) {
   QOpcUaNode *rpmNode = client->node(results.at(0).targetId());
   if (!rpmNode) {
       qWarning() << "Failed to create node";
       return;
   }
   // Connect slots, call methods
} else {
    qWarning() << "Browse path could not be fully resolved, the target node is on another server";
    return;
}
PySide6.QtOpcUa.QOpcUaNode.resolveBrowsePathFinished(targets, path, statusCode)#
Parameters
PySide6.QtOpcUa.QOpcUaNode.serverTimestamp(attribute)#
Parameters

attributeNodeAttribute

Return type

PySide6.QtCore.QDateTime

Returns the server timestamp from the last read or data change of attribute. Before at least one attributeRead or dataChangeOccurred signal has been emitted, a null datetime is returned.

PySide6.QtOpcUa.QOpcUaNode.sourceTimestamp(attribute)#
Parameters

attributeNodeAttribute

Return type

PySide6.QtCore.QDateTime

Returns the source timestamp from the last read or data change of attribute. Before at least one attributeRead or dataChangeOccurred signal has been emitted, a null datetime is returned.

PySide6.QtOpcUa.QOpcUaNode.valueAttribute()#
Return type

object

Returns the value of the node’s Value attribute.

The returned value is only valid after the Value attribute has been successfully read or written or after a data change from a monitoring has updated the attribute cache. This is indicated by a attributeRead() or attributeWritten() signal with status code Good or a dataChangeOccurred() signal for the Value attribute.

If there is no value in the attribute cache, an invalid QVariant is returned.

PySide6.QtOpcUa.QOpcUaNode.valueAttributeError()#
Return type

UaStatusCode

Returns the error code for the node’s Value attribute. The status code Good indicates a valid return value for valueAttribute() . If there is no entry in the attribute cache, BadNoEntryExists is returned.

PySide6.QtOpcUa.QOpcUaNode.writeAttribute(attribute, value[, type=QOpcUa.Types.Undefined])#
Parameters
Return type

bool

Writes value to the attribute given in attribute using the type information from type. Returns true if the asynchronous call has been successfully dispatched.

If the type parameter is omitted, the backend tries to find the correct type. The following default types are assumed:

Qt MetaType

OPC UA type

Bool

Boolean

UChar

Byte

Char

SByte

UShort

UInt16

Short

Int16

Int

Int32

UInt

UInt32

ULongLong

UInt64

LongLong

Int64

Double

Double

Float

Float

QString

String

QDateTime

DateTime

QByteArray

ByteString

QUuid

Guid

PySide6.QtOpcUa.QOpcUaNode.writeAttributeRange(attribute, value, indexRange[, type=QOpcUa.Types.Undefined])#
Parameters
Return type

bool

Writes value to the attribute given in attribute using the type information from type. For indexRange, see readAttributeRange() .

Returns true if the asynchronous call has been successfully dispatched.

PySide6.QtOpcUa.QOpcUaNode.writeAttributes(toWrite[, valueAttributeType=QOpcUa.Types.Undefined])#
Parameters
  • toWrite

  • valueAttributeTypeTypes

Return type

bool

Executes a write operation for the attributes and values specified in toWrite.

Returns true if the asynchronous call has been successfully dispatched.

The valueAttributeType parameter can be used to supply type information for the value attribute. All other attributes have known types.

See also

writeAttribute()

PySide6.QtOpcUa.QOpcUaNode.writeValueAttribute(value[, type=QOpcUa.Types.Undefined])#
Parameters
  • value – object

  • typeTypes

Return type

bool

Writes value to the node’s Value attribute using the type information from type.

Returns true if the asynchronous call has been successfully dispatched.

See also

writeAttribute()