class QOpcUaNode

QOpcUaNode allows interaction with an OPC UA node. More…

Inheritance diagram of PySide6.QtOpcUa.QOpcUaNode

Synopsis

Methods

Signals

Static functions

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 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.
static allBaseAttributes()
Return type:

Combination of NodeAttribute

Contains all attributes of the OPC UA base node class.

attribute(attribute)
Parameters:

attribute – NodeAttribute

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.

attributeError(attribute)
Parameters:

attribute – NodeAttribute

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

attributeRead(attributes)
Parameters:

attributes – Combination of NodeAttribute

This signal is emitted after a readAttributes() or readAttributeRange() operation has finished. The receiver has to check the status code for the attributes contained in attributes.

attributeUpdated(attr, value)
Parameters:

This signal is emitted after the value in the attribute cache has been updated by a data change notification from the server, a read or a write operation. value contains the new value for the node attribute attr.

attributeWritten(attribute, statusCode)
Parameters:

This signal is emitted after a writeAttribute() , writeAttributes() or writeAttributeRange() operation has finished.

Before this signal is emitted, the attribute cache is updated in case of a successful write. For writeAttributes() a signal is emitted for each attribute in the write call. statusCode contains the success information for the write operation on attribute.

browse(request)
Parameters:

request – 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);
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.

browseFinished(children, statusCode)
Parameters:

  • children – .list of QOpcUaReferenceDescription

  • statusCode – UaStatusCode

This signal is emitted after a browseChildren() or browse() operation has finished.

children contains information about all nodes which matched the criteria in browseChildren() . statusCode contains the service result of the browse operation. If statusCode is not Good , the passed children vector is empty.

callMethod(methodNodeId[, args=list()])
Parameters:

  • methodNodeId – str

  • args – .list of std.pairQVariant,QOpcUa.Types

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.

client()
Return type:

QOpcUaClient

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

dataChangeOccurred(attr, value)
Parameters:

This signal is emitted after a data change notification has been received. value contains the new value for the node attribute attr.

disableMonitoring(attr)
Parameters:

attr – Combination of NodeAttribute

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.

disableMonitoringFinished(attr, statusCode)
Parameters:

This signal is emitted after an asynchronous call to disableMonitoring() has finished. statusCode contains the status code generated by the operation. After this signal has been emitted, monitoringStatus returns a default constructed value with status code BadMonitoredItemIdIinvalid for attr.

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 ).

enableMonitoringFinished(attr, statusCode)
Parameters:

This signal is emitted after an asynchronous call to enableMonitoring() has finished. After this signal has been emitted, monitoringStatus() returns valid information for attr. statusCode contains the status code for the operation.

eventOccurred(eventFields)
Parameters:

eventFields – .list of QVariant

This signal is emitted after a new event has been received.

eventFields contains the values of the event fields in the order specified in the select clause of the event filter.

static mandatoryBaseAttributes()
Return type:

Combination of NodeAttribute

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

methodCallFinished(methodNodeId, result, statusCode)
Parameters:

  • methodNodeId – str

  • result – object

  • statusCode – UaStatusCode

This signal is emitted after a method call for methodNodeId has finished on the server. statusCode contains the status code from the method call, result contains the output arguments of the method. result is empty if the method has no output arguments or statusCode is not Good . The result variant is either a single value if there is only one output argument or it contains a list of variants in case the called function returned multiple output arguments.

if (result.canConvert<QVariantList>()) {
    // handle list type
} else {
    // handle value type
}
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.

modifyEventFilter(eventFilter)
Parameters:

eventFilter – 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.

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.

monitoringStatus(attr)
Parameters:

attr – NodeAttribute

Return type:

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 .

monitoringStatusChanged(attr, items, statusCode)
Parameters:

This signal is emitted after an asynchronous call to modifyMonitoring() has finished. The node attribute for which the operation was requested is returned in attr. items contains the parameters that have been modified. statusCode contains the result of the modify operation on the server.

nodeId()
Return type:

str

Returns the ID of the OPC UA node.

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 1.05 part 4, 7.27. 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.

readAttributes([attributes=QOpcUaNode.mandatoryBaseAttributes()])
Parameters:

attributes – Combination of NodeAttribute

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.

readHistoryEvents(startTime, endTime, filter[, numValues=0])
Parameters:
Return type:

QOpcUaHistoryReadResponse

Starts a read event history request for this node using the parameters startTime, endTime, filter and numValues. The filter is used by the server to determine which events and which set of their fields shall be returned.

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.

The following example retrieves historic events for the last two days. Up to 10 events are returned at a time. While there are more events matching the filter and the provided time range, hasMoreData() will be true and more events can be fetched via readMoreData().

QScopedPointer<QOpcUaNode> node(opcuaClient->node("ns=2;s=EventHistorian"));
QVERIFY(node != nullptr);

QOpcUaMonitoringParameters::EventFilter filter;
filter << QOpcUaSimpleAttributeOperand("Message");
filter << QOpcUaSimpleAttributeOperand("Time");

const auto response = node->readHistoryEvents(QDateTime::currentDateTime().addDays(-2), QDateTime::currentDateTime(), filter, 10);

QObject::connect(response, &QOpcUaHistoryReadResponse::readHistoryEventsFinished, this,
                 [response](const QList<QOpcUaHistoryEvent> &results, QOpcUa::UaStatusCode serviceResult) {
                     if (serviceResult != QOpcUa::UaStatusCode::Good) {
                         qDebug() << "Service call failed with" << serviceResult;
                         return;
                     }

                     // Print what we got so far
                     for (const auto &result : response->events()) {
                         qDebug() << "Results for" << result.nodeId() << result.statusCode();
                         for (const auto &event : result.events())
                             qDebug() << "    Event:" << event;
                     }

                     if (response->hasMoreData())
                         response->readMoreData();
                 });
readHistoryRaw(startTime, endTime, numValues, returnBounds)
Parameters:
Return type:

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 1.05 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();
            }
        }
    });
}
readHistoryRaw(startTime, endTime, numValues, returnBounds, timestampsToReturn)
Parameters:
Return type:

QOpcUaHistoryReadResponse

Starts a read history request for this node. The additional timestampsToReturn parameter determines which timestamps will be returned for each value.

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()

resolveBrowsePath(path)
Parameters:

path – .list of QOpcUaRelativePathElement

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 1.05 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;
}
resolveBrowsePathFinished(targets, path, statusCode)
Parameters:

  • targets – .list of QOpcUaBrowsePathTarget

  • path – .list of QOpcUaRelativePathElement

  • statusCode – UaStatusCode

This signal is emitted after a resolveBrowsePath() call has finished.

QOpcUaBrowsePathTarget targets contains the matches, statusCode is the status code of the operation. If statusCode is not Good , targets is empty. The browse path path is the browse path from the request. It can be used to associate results with requests.

serverTimestamp(attribute)
Parameters:

attribute – NodeAttribute

Return type:

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.

sourceTimestamp(attribute)
Parameters:

attribute – NodeAttribute

Return type:

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.

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.

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.

valueAttributeUpdated(value)
Parameters:

value – object

This signal is emitted after the value attribute in the attribute cache has been updated by a data change notification from the server, a read or a write operation. value contains the new value for the value attribute.

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
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.

writeAttributes(toWrite[, valueAttributeType=QOpcUa.Types.Undefined])
Parameters:

  • toWrite – Dictionary with keys of type .QOpcUa.NodeAttribute and values of type QVariant.

  • valueAttributeType – Types

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()

writeValueAttribute(value[, type=QOpcUa.Types.Undefined])
Parameters:

  • value – object

  • type – Types

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()