events/client_eventfilter.cpp

// This example should be executed while `server_events` is running. You can use e.g. UaExpert to
// trigger events with custom severity and messages using the `GenerateEvent` method node.
 
#include <iostream>
 
#include <open62541pp/client.hpp>
#include <open62541pp/node.hpp>
#include <open62541pp/subscription.hpp>
 
int main() {
    opcua::Client client;
    client.connect("opc.tcp://localhost:4840");
 
    // Define filter elements
    const opcua::ContentFilterElement filterBaseEventType{
        opcua::FilterOperator::OfType,
        {
            opcua::LiteralOperand{opcua::NodeId{opcua::ObjectTypeId::BaseEventType}},
        }
    };
    const opcua::ContentFilterElement filterLowSeverity{
        opcua::FilterOperator::LessThan,
        {
            opcua::SimpleAttributeOperand(
                opcua::ObjectTypeId::BaseEventType, {{0, "Severity"}}, opcua::AttributeId::Value
            ),
            opcua::LiteralOperand{200},
        }
    };
 
    // Combine filter with unary operators (!) and binary operators (&&, ||).
    // The resulting filter will filter events of type BaseEventType with severity >= 200.
    const opcua::ContentFilter filterCombined = filterBaseEventType && !filterLowSeverity;
 
    const opcua::EventFilter eventFilter{
        // Select clause
        {
            {opcua::ObjectTypeId::BaseEventType, {{0, "Time"}}, opcua::AttributeId::Value},
            {opcua::ObjectTypeId::BaseEventType, {{0, "Severity"}}, opcua::AttributeId::Value},
            {opcua::ObjectTypeId::BaseEventType, {{0, "Message"}}, opcua::AttributeId::Value},
        },
        // Where clause
        filterCombined
    };
 
    opcua::Subscription sub{client};
    sub.subscribeEvent(
        opcua::ObjectId::Server,
        eventFilter,
        [&](opcua::IntegerId subId,
            opcua::IntegerId monId,
            opcua::Span<const opcua::Variant> eventFields) {
            opcua::MonitoredItem item{client, subId, monId};
            std::cout
                << "Event notification:\n"
                << "- subscription id:   " << item.subscriptionId() << "\n"
                << "- monitored item id: " << item.monitoredItemId() << "\n"
                << "- node id:           " << opcua::toString(item.nodeId()) << "\n"
                << "- attribute id:      " << static_cast<int>(item.attributeId()) << "\n";
 
            const auto& time = eventFields.at(0).scalar<opcua::DateTime>();
            const auto& severity = eventFields.at(1).scalar<uint16_t>();
            const auto& message = eventFields.at(2).scalar<opcua::LocalizedText>();
 
            std::cout << "Time:     " << time.format("%Y-%m-%d %H:%M:%S") << "\n";
            std::cout << "Severity: " << severity << "\n";
            std::cout << "Message:  " << message.text() << "\n";
        }
    );
 
    // Run the client's main loop to process callbacks and events.
    // This will block until client.stop() is called or an exception is thrown.
    client.run();
}