OPC Studio User's Guide and Reference
WhereClause Property (UAEventFilter)
Example 



OpcLabs.EasyOpcUA Assembly > OpcLabs.EasyOpc.UA Namespace > UAEventFilter Class : WhereClause Property
The criteria limiting the Notifications.
Syntax
'Declaration
 
<DataMemberAttribute()>
<DefaultValueAttribute(Mono.Cecil.CustomAttributeArgument)>
Public Property WhereClause As UAContentFilterElement
'Usage
 
Dim instance As UAEventFilter
Dim value As UAContentFilterElement
 
instance.WhereClause = value
 
value = instance.WhereClause
[DataMember()]
[DefaultValue(Mono.Cecil.CustomAttributeArgument)]
public UAContentFilterElement WhereClause {get; set;}
[DataMember()]
[DefaultValue(Mono.Cecil.CustomAttributeArgument)]
public:
property UAContentFilterElement^ WhereClause {
   UAContentFilterElement^ get();
   void set (    UAContentFilterElement^ value);
}
Remarks

In order to obtain or modify this parameter, access the UAMonitoringParameters.EventFilter property of OpcLabs.EasyOpc.UA.OperationModel.UAMonitoredItemArguments.MonitoringParameters.

This method or property does not throw any exceptions, aside from execution exceptions such as System.Threading.ThreadAbortException or System.OutOfMemoryException.

Example

.NET

COM

// This example shows how to specify criteria for event notifications.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

using System;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.AddressSpace;
using OpcLabs.EasyOpc.UA.AddressSpace.Standard;
using OpcLabs.EasyOpc.UA.AlarmsAndConditions;
using OpcLabs.EasyOpc.UA.Filtering;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples.AlarmsAndConditions
{
    class WhereClause
    {
        public static void Main1()
        {
            UAEndpointDescriptor endpointDescriptor =
                "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer";

            // Instantiate the client object and hook events.
            var client = new EasyUAClient();
            client.EventNotification += client_EventNotification;

            Console.WriteLine("Subscribing...");
            client.SubscribeEvent(
                endpointDescriptor,
                UAObjectIds.Server,
                1000,
                new UAEventFilterBuilder(
                    // Either the severity is >= 500, or the event comes from a specified source node
                    UAFilterElements.Or(
                        UAFilterElements.GreaterThanOrEqual(UABaseEventObject.Operands.Severity, 500),
                        UAFilterElements.Equals(
                            UABaseEventObject.Operands.SourceNode, 
                            new UANodeId("nsu=http://opcfoundation.org/Quickstarts/AlarmCondition ;ns=2;s=1:Metals/SouthMotor"))),
                    UABaseEventObject.AllFields));

            Console.WriteLine("Processing event notifications for 30 seconds...");
            System.Threading.Thread.Sleep(30 * 1000);

            Console.WriteLine("Unsubscribing...");
            client.UnsubscribeAllMonitoredItems();

            Console.WriteLine("Waiting for 5 seconds...");
            System.Threading.Thread.Sleep(5 * 1000);

            Console.WriteLine("Finished.");
        }

        static void client_EventNotification(object sender, EasyUAEventNotificationEventArgs e)
        {
            // Display the event.
            Console.WriteLine(e);
        }


        // Example output:
        //
        //Subscribing...
        //13000008
        //Processing event notifications for 30 seconds...
        //[] Success
        //[] Success; Refresh; RefreshInitiated
        //[] Success; Refresh; [SouthMotor] 100! {DialogConditionType} "The dialog was activated" @9/9/2021 2:22:18 PM (10 fields)
        //[] Success; Refresh; [SouthMotor] 700! {ExclusiveDeviationAlarmType} "The alarm severity has increased." @9/22/2021 7:17:59 AM (10 fields)
        //[] Success; Refresh; [SouthMotor] 900! {NonExclusiveLevelAlarmType} "The alarm severity has increased." @9/22/2021 7:17:57 AM (10 fields)
        //[] Success; Refresh; [SouthMotor] 100! {TripAlarmType} "The alarm is active." @9/22/2021 7:17:59 AM (10 fields)
        //[] Success; Refresh; [SouthMotor] 100! {TripAlarmType} "The alarm severity has increased." @9/9/2021 3:39:51 PM (10 fields)
        //[] Success; Refresh; [SouthMotor] 100! {TripAlarmType} "The alarm severity has increased." @9/9/2021 3:38:57 PM (10 fields)
        //[] Success; Refresh; RefreshComplete
        //[] Success; [SouthMotor] 100! {NonExclusiveLevelAlarmType} "The alarm was deactivated by the system." @9/22/2021 7:18:05 AM (10 fields)
        //[] Success; [SouthMotor] 300! {TripAlarmType} "The alarm severity has increased." @9/22/2021 7:18:08 AM (10 fields)
        //[] Success; [SouthMotor] 900! {ExclusiveDeviationAlarmType} "The alarm severity has increased." @9/22/2021 7:18:10 AM (10 fields)
        //[] Success; [SouthMotor] 100! {NonExclusiveLevelAlarmType} "The alarm is active." @9/22/2021 7:18:13 AM (10 fields)
        //[] Success; [SouthMotor] 500! {TripAlarmType} "The alarm severity has increased." @9/22/2021 7:18:17 AM (10 fields)
        //[] Success; [SouthMotor] 100! {ExclusiveDeviationAlarmType} "The alarm was deactivated by the system." @9/22/2021 7:18:21 AM (10 fields)
        //[] Success; [SouthMotor] 300! {NonExclusiveLevelAlarmType} "The alarm severity has increased." @9/22/2021 7:18:21 AM (10 fields)
        //[] Success; [SouthMotor] 700! {TripAlarmType} "The alarm severity has increased." @9/22/2021 7:18:26 AM (10 fields)
        //[] Success; [SouthMotor] 500! {NonExclusiveLevelAlarmType} "The alarm severity has increased." @9/22/2021 7:18:29 AM (10 fields)
        //[] Success; [SouthMotor] 100! {ExclusiveDeviationAlarmType} "The alarm is active." @9/22/2021 7:18:32 AM (10 fields)
        //Unsubscribing...
        //Waiting for 5 seconds...
        //Finished.
    }
}
# This example shows how to specify criteria for event notifications.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

#requires -Version 5.1
using namespace OpcLabs.EasyOpc.UA
using namespace OpcLabs.EasyOpc.UA.AddressSpace
using namespace OpcLabs.EasyOpc.UA.AddressSpace.Standard

# The path below assumes that the current directory is [ProductDir]/Examples-NET/PowerShell/Windows .
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcUA.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcUAComponents.dll"

# Define which server we will work with.
[UAEndpointDescriptor]$endpointDescriptor = "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer"

# Instantiate the client object.
$client = New-Object EasyUAClient

# Event notification handler
Register-ObjectEvent -InputObject $client -EventName EventNotification -Action { 
    # Display the event.
    Write-Host $EventArgs
}

Write-Host "Subscribing..."
[IEasyUAClientExtension]::SubscribeEvent($client, 
    $endpointDescriptor, 
    [UAObjectIds]::Server, 
    1000,
    [UAEventFilter](New-Object UAEventFilterBuilder(
        [UAFilterElements]::Equals(
            [UABaseEventObject+Operands]::SourceNode, 
            (New-Object UANodeId("nsu=http://opcfoundation.org/Quickstarts/AlarmCondition ;ns=2;s=1:Metals/SouthMotor"))),
        [UABaseEventObject]::AllFields))
    )

Write-Host "Processing event notifications for 30 seconds..."
$stopwatch =  [System.Diagnostics.Stopwatch]::StartNew() 
while ($stopwatch.Elapsed.TotalSeconds -lt 30) {    
    Start-Sleep -Seconds 1
}

Write-Host "Unsubscribing..."
$client.UnsubscribeAllMonitoredItems()

Write-Host "Waiting for 5 seconds..."
Start-Sleep -Seconds 5

Write-Host "Finished."


# Example output:
#
#Subscribing...
#13000008
#Processing event notifications for 30 seconds...
#[] Success
#[] Success; Refresh; RefreshInitiated
#[] Success; Refresh; [SouthMotor] 100! {DialogConditionType} "The dialog was activated" @9/9/2021 2:22:18 PM (10 fields)
#[] Success; Refresh; [SouthMotor] 700! {ExclusiveDeviationAlarmType} "The alarm severity has increased." @9/22/2021 7:17:59 AM (10 fields)
#[] Success; Refresh; [SouthMotor] 900! {NonExclusiveLevelAlarmType} "The alarm severity has increased." @9/22/2021 7:17:57 AM (10 fields)
#[] Success; Refresh; [SouthMotor] 100! {TripAlarmType} "The alarm is active." @9/22/2021 7:17:59 AM (10 fields)
#[] Success; Refresh; [SouthMotor] 100! {TripAlarmType} "The alarm severity has increased." @9/9/2021 3:39:51 PM (10 fields)
#[] Success; Refresh; [SouthMotor] 100! {TripAlarmType} "The alarm severity has increased." @9/9/2021 3:38:57 PM (10 fields)
#[] Success; Refresh; RefreshComplete
#[] Success; [SouthMotor] 100! {NonExclusiveLevelAlarmType} "The alarm was deactivated by the system." @9/22/2021 7:18:05 AM (10 fields)
#[] Success; [SouthMotor] 300! {TripAlarmType} "The alarm severity has increased." @9/22/2021 7:18:08 AM (10 fields)
#[] Success; [SouthMotor] 900! {ExclusiveDeviationAlarmType} "The alarm severity has increased." @9/22/2021 7:18:10 AM (10 fields)
#[] Success; [SouthMotor] 100! {NonExclusiveLevelAlarmType} "The alarm is active." @9/22/2021 7:18:13 AM (10 fields)
#[] Success; [SouthMotor] 500! {TripAlarmType} "The alarm severity has increased." @9/22/2021 7:18:17 AM (10 fields)
#[] Success; [SouthMotor] 100! {ExclusiveDeviationAlarmType} "The alarm was deactivated by the system." @9/22/2021 7:18:21 AM (10 fields)
#[] Success; [SouthMotor] 300! {NonExclusiveLevelAlarmType} "The alarm severity has increased." @9/22/2021 7:18:21 AM (10 fields)
#[] Success; [SouthMotor] 700! {TripAlarmType} "The alarm severity has increased." @9/22/2021 7:18:26 AM (10 fields)
#[] Success; [SouthMotor] 500! {NonExclusiveLevelAlarmType} "The alarm severity has increased." @9/22/2021 7:18:29 AM (10 fields)
#[] Success; [SouthMotor] 100! {ExclusiveDeviationAlarmType} "The alarm is active." @9/22/2021 7:18:32 AM (10 fields)
#Unsubscribing...
#Waiting for 5 seconds...
#Finished.
# This example shows how to specify criteria for event notifications.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
# OPC client and subscriber examples in Python on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-Python .
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time

# Import .NET namespaces.
from OpcLabs.EasyOpc.UA import *
from OpcLabs.EasyOpc.UA.AddressSpace import *
from OpcLabs.EasyOpc.UA.AddressSpace.Standard import *
from OpcLabs.EasyOpc.UA.AlarmsAndConditions import *
from OpcLabs.EasyOpc.UA.Filtering import *
from OpcLabs.EasyOpc.UA.OperationModel import *


def eventNotification(sender, eventArgs):
    # Display the event.
    print(eventArgs)


# Define which server we will work with.
endpointDescriptor = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer')

# Instantiate the client object and hook events.
client = EasyUAClient()
client.EventNotification += eventNotification

print('Subscribing...')

eventFilterBuilder = UAEventFilterBuilder(
    # Either the severity is >= 500, or the event comes from a specified source node.
    UAFilterElements.Or(
        UAFilterElements.GreaterThanOrEqual(UABaseEventObject.Operands.Severity, 500),
        UAFilterElements.Equals(
            UABaseEventObject.Operands.SourceNode,
            UANodeId('nsu=http://opcfoundation.org/Quickstarts/AlarmCondition ;ns=2;s=1:Metals/SouthMotor'))),
    UABaseEventObject.AllFields)

IEasyUAClientExtension.SubscribeEvent(
    client,
    endpointDescriptor,
    UANodeDescriptor(UAObjectIds.Server),
    1000,
    UAEventFilterBuilder.ToUAEventFilter(eventFilterBuilder))

print('Processing event notifications for 30 seconds...')
time.sleep(30)

print('Unsubscribing...')
client.UnsubscribeAllMonitoredItems()

print('Waiting for 5 seconds...')
time.sleep(5)

print('Finished.')
// This example shows how to specify criteria for event notifications.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

type
  TClientEventHandlers3 = class
    procedure OnEventNotification(
      Sender: TObject;
      sender0: OleVariant;
      eventArgs: _EasyUAEventNotificationEventArgs);
  end;

procedure TClientEventHandlers3.OnEventNotification(
  Sender: TObject;
  sender0: OleVariant;
  eventArgs: _EasyUAEventNotificationEventArgs);
begin
  // Display the event
  WriteLn(eventArgs.ToString);
end;

class procedure WhereClause.Main;

  function ToUAAttributeField(Operand: UASimpleAttributeOperand): UAAttributeField;
  var
    AttributeField: UAAttributeField;
  begin
    AttributeField := CoUAAttributeField.Create;
    AttributeField.Operand := Operand;
    ToUAAttributeField := AttributeField;
  end;

  function ObjectTypeIds_BaseEventType: UANodeId;
  var
    NodeId: UANodeId;
  begin
    NodeId := CoUANodeId.Create;
    NodeId.StandardName := 'BaseEventType';
    ObjectTypeIds_BaseEventType := NodeId;
  end;

  function UAFilterElements_SimpleAttribute(TypeId: UANodeId; SimpleRelativeBrowsePathString: string): UASimpleAttributeOperand;
  var
    Operand: UASimpleAttributeOperand;
    BrowsePathParser: UABrowsePathParser;
  begin
    BrowsePathParser := CoUABrowsePathParser.Create;
    Operand := CoUASimpleAttributeOperand.Create;
    Operand.TypeId.NodeId := TypeId;
    Operand.QualifiedNames := BrowsePathParser.ParseRelative(SimpleRelativeBrowsePathString).ToUAQualifiedNameCollection;
    UAFilterElements_SimpleAttribute := Operand;
  end;

  function UABaseEventObject_Operands_NodeId: UASimpleAttributeOperand;
  var
    Operand: UASimpleAttributeOperand;
  begin
    Operand := CoUASimpleAttributeOperand.Create;
    Operand.TypeId.NodeId.StandardName := 'BaseEventType';
    Operand.AttributeId := UAAttributeId_NodeId;
    UABaseEventObject_Operands_NodeId := Operand;
  end;

  function UABaseEventObject_Operands_EventId: UASimpleAttributeOperand;
  begin
    UABaseEventObject_Operands_EventId := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/EventId');
  end;

  function UABaseEventObject_Operands_EventType: UASimpleAttributeOperand;
  begin
    UABaseEventObject_Operands_EventType := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/EventType');
  end;

  function UABaseEventObject_Operands_SourceNode: UASimpleAttributeOperand;
  begin
    UABaseEventObject_Operands_SourceNode := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/SourceNode');
  end;

  function UABaseEventObject_Operands_SourceName: UASimpleAttributeOperand;
  begin
    UABaseEventObject_Operands_SourceName := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/SourceName');
  end;

  function UABaseEventObject_Operands_Time: UASimpleAttributeOperand;
  begin
    UABaseEventObject_Operands_Time := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/Time');
  end;

  function UABaseEventObject_Operands_ReceiveTime: UASimpleAttributeOperand;
  begin
    UABaseEventObject_Operands_ReceiveTime := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/ReceiveTime');
  end;

  function UABaseEventObject_Operands_LocalTime: UASimpleAttributeOperand;
  begin
    UABaseEventObject_Operands_LocalTime := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/LocalTime');
  end;

  function UABaseEventObject_Operands_Message: UASimpleAttributeOperand;
  begin
    UABaseEventObject_Operands_Message := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/Message');
  end;

  function UABaseEventObject_Operands_Severity: UASimpleAttributeOperand;
  begin
    UABaseEventObject_Operands_Severity := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/Severity');
  end;

  function UABaseEventObject_AllFields: UAAttributeFieldCollection;
  var
    Fields: UAAttributeFieldCollection;
  begin
    Fields := CoUAAttributeFieldCollection.Create;

    Fields.Add(ToUAAttributeField(UABaseEventObject_Operands_NodeId));

    Fields.Add(ToUAAttributeField(UABaseEventObject_Operands_EventId));
    Fields.Add(ToUAAttributeField(UABaseEventObject_Operands_EventType));
    Fields.Add(ToUAAttributeField(UABaseEventObject_Operands_SourceNode));
    Fields.Add(ToUAAttributeField(UABaseEventObject_Operands_SourceName));
    Fields.Add(ToUAAttributeField(UABaseEventObject_Operands_Time));
    Fields.Add(ToUAAttributeField(UABaseEventObject_Operands_ReceiveTime));
    Fields.Add(ToUAAttributeField(UABaseEventObject_Operands_LocalTime));
    Fields.Add(ToUAAttributeField(UABaseEventObject_Operands_Message));
    Fields.Add(ToUAAttributeField(UABaseEventObject_Operands_Severity));

    UABaseEventObject_AllFields := Fields;
  end;

var
  Arguments: OleVariant;
  EvsClient: TEvsEasyUAClient;
  Client: EasyUAClient;
  ClientEventHandlers: TClientEventHandlers3;
  Handle: Cardinal;
  HandleArray: OleVariant;
  MonitoredItemArguments: EasyUAMonitoredItemArguments;
  MonitoringParameters: UAMonitoringParameters;
  EventFilter: UAEventFilter;
  WhereClause: UAContentFilterElement;
  Operand1: UASimpleAttributeOperand;
  Operand2: UALiteralOperand;
  Operand3: UASimpleAttributeOperand;
  Operand4: UALiteralOperand;
  SourceNodeId: UANodeId;
  Element1, Element2: UAContentFilterElement;
  BaseEventType: UANodeId;
begin
  // Instantiate the client object and hook events
  EvsClient := TEvsEasyUAClient.Create(nil);
  Client := EvsClient.ComServer;
  ClientEventHandlers := TClientEventHandlers3.Create;
  EvsClient.OnEventNotification := @ClientEventHandlers.OnEventNotification;

  WriteLn('Subscribing...');

  WhereClause := CoUAContentFilterElement.Create;
  BaseEventType := CoUaNodeId.Create;
  BaseEventType.StandardName := 'BaseEventType';

  // Either the severity is >= 500, or the event comes from a specified source node
  Operand1 := UABaseEventObject_Operands_Severity;
  Operand2 := CoUALiteralOperand.Create;
  Operand2.Value := 500;
  Element1 := CoUAContentFilterElement.Create;
  Element1.FilterOperator := UAFilterOperator_GreaterThanOrEqual;
  Element1.FilterOperands.Add(Operand1);
  Element1.FilterOperands.Add(Operand2);
  Operand3 := UABaseEventObject_Operands_SourceNode;
  SourceNodeId := CoUANodeId.Create;
  SourceNodeId.ExpandedText := 'nsu=http://opcfoundation.org/Quickstarts/AlarmCondition;ns=2;s=1:Metals/SouthMotor';
  Operand4 := CoUALiteralOperand.Create;
  Operand4.Value := SourceNodeId;
  Element2 := CoUAContentFilterElement.Create;
  Element2.FilterOperator := UAFilterOperator_Equals;
  Element2.FilterOperands.Add(Operand3);
  Element2.FilterOperands.Add(Operand4);
  WhereClause.FilterOperator := UAFilterOperator_Or;
  WhereClause.FilterOperands.Add(Element1);
  WhereClause.FilterOperands.Add(Element2);

  EventFilter := CoUAEventFilter.Create;
  EventFilter.SelectClauses := UABaseEventObject_AllFields;
  EventFilter.WhereClause := WhereClause;

  MonitoringParameters := CoUAMonitoringParameters.Create;
  MonitoringParameters.SamplingInterval := 1000;
  MonitoringParameters.EventFilter := EventFilter;
  MonitoringParameters.QueueSize := 1000;

  MonitoredItemArguments := CoEasyUAMonitoredItemArguments.Create;
  MonitoredItemArguments.EndpointDescriptor.UrlString := 'opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer';
  MonitoredItemArguments.NodeDescriptor.NodeId.StandardName := 'Server';
  MonitoredItemArguments.MonitoringParameters := MonitoringParameters;
  //MonitoredItemArguments.SubscriptionParameters.PublishingInterval := 0;
  MonitoredItemArguments.AttributeId := UAAttributeId_EventNotifier;

  Arguments := VarArrayCreate([0, 0], varVariant);
  Arguments[0] := MonitoredItemArguments;

  TVarData(HandleArray).VType := varArray or varVariant;
  TVarData(HandleArray).VArray := PVarArray(
    Client.SubscribeMultipleMonitoredItems(PSafeArray(TVarData(Arguments).VArray)));

  WriteLn('Processing event notifications for 30 seconds...');
  PumpSleep(30*1000);

  WriteLn('Unsubscribing...');
  Client.UnsubscribeAllMonitoredItems;

  WriteLn('Waiting for 5 seconds...');
  PumpSleep(5*1000);

  WriteLn('Finished...');
end;
// This example shows how to specify criteria for event notifications.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

type
  THelperMethods10 = class
    class function ObjectTypeIds_BaseEventType: _UANodeId; static;
    class function UABaseEventObject_Operands_EventId: _UASimpleAttributeOperand; static;
    class function UABaseEventObject_Operands_EventType: _UASimpleAttributeOperand; static;
    class function UABaseEventObject_Operands_NodeId: _UASimpleAttributeOperand; static;
    class function UAFilterElements_SimpleAttribute(TypeId: _UANodeId; simpleRelativeBrowsePathString: string): _UASimpleAttributeOperand; static;
    class function UABaseEventObject_Operands_SourceName: _UASimpleAttributeOperand; static;
    class function UABaseEventObject_Operands_Time: _UASimpleAttributeOperand; static;
    class function UABaseEventObject_Operands_ReceiveTime: _UASimpleAttributeOperand; static;
    class function UABaseEventObject_Operands_LocalTime: _UASimpleAttributeOperand;
    class function UABaseEventObject_Operands_SourceNode: _UASimpleAttributeOperand; static;
    class function UABaseEventObject_Operands_Message: _UASimpleAttributeOperand; static;
    class function UABaseEventObject_Operands_Severity: _UASimpleAttributeOperand; static;
    class function UABaseEventObject_AllFields: _UAAttributeFieldCollection; static;
  end;

type
  TClientEventHandlers10 = class
    procedure Client_EventNotification(
      ASender: TObject;
      sender: OleVariant;
      const eventArgs: _EasyUAEventNotificationEventArgs);
  end;

procedure TClientEventHandlers10.Client_EventNotification(
  ASender: TObject;
  sender: OleVariant;
  const eventArgs: _EasyUAEventNotificationEventArgs);
begin
  // Display the event
  WriteLn(eventArgs.ToString);
end;

class procedure WhereClause.Main;
const
  UAObjectIds_Server = 'nsu=http://opcfoundation.org/UA/;i=2253';
var
  Arguments: OleVariant;
  Client: TEasyUAClient;
  ClientEventHandlers: TClientEventHandlers10;
  Element1, Element2: _UAContentFilterElement;
  EndpointDescriptor: string;
  EventFilter: _UAEventFilter;
  MonitoredItemArguments: _EasyUAMonitoredItemArguments;
  MonitoringParameters: _UAMonitoringParameters;
  Operand1, Operand3: _UASimpleAttributeOperand;
  Operand2, Operand4: _UALiteralOperand;
  SourceNodeId: _UANodeId;
  WhereClause: _UAContentFilterElement;
begin
  EndpointDescriptor := 'opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer';

  // Instantiate the client object and hook events
  Client := TEasyUAClient.Create(nil);
  ClientEventHandlers := TClientEventHandlers10.Create;
  Client.OnEventNotification := ClientEventHandlers.Client_EventNotification;

  WriteLn('Subscribing...');

  WhereClause := CoUAContentFilterElement.Create;

  // Either the severity is >= 500, or the event comes from a specified source node
  Operand1 := THelperMethods10.UABaseEventObject_Operands_Severity;
  Operand2 := CoUALiteralOperand.Create;
  Operand2.Value := 500;
  Element1 := CoUAContentFilterElement.Create;
  Element1.FilterOperator := UAFilterOperator_GreaterThanOrEqual;
  Element1.FilterOperands.Add(Operand1);
  Element1.FilterOperands.Add(Operand2);
  Operand3 := THelperMethods10.UABaseEventObject_Operands_SourceNode;
  SourceNodeId := CoUANodeId.Create;
  SourceNodeId.ExpandedText := 'nsu=http://opcfoundation.org/Quickstarts/AlarmCondition;ns=2;s=1:Metals/SouthMotor';
  Operand4 := CoUALiteralOperand.Create;
  Operand4.Value := SourceNodeId;
  Element2 := CoUAContentFilterElement.Create;
  Element2.FilterOperator := UAFilterOperator_Equals;
  Element2.FilterOperands.Add(Operand3);
  Element2.FilterOperands.Add(Operand4);
  WhereClause.FilterOperator := UAFilterOperator_Or;
  WhereClause.FilterOperands.Add(Element1);
  WhereClause.FilterOperands.Add(Element2);

  EventFilter := CoUAEventFilter.Create;
  EventFilter.SelectClauses := THelperMethods10.UABaseEventObject_AllFields;
  EventFilter.WhereClause := WhereClause;

  MonitoringParameters := CoUAMonitoringParameters.Create;
  MonitoringParameters.SamplingInterval := 1000;
  MonitoringParameters.EventFilter := EventFilter;
  MonitoringParameters.QueueSize := 1000;

  MonitoredItemArguments := CoEasyUAMonitoredItemArguments.Create;
  MonitoredItemArguments.EndpointDescriptor.UrlString := 'opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer';
  MonitoredItemArguments.NodeDescriptor.NodeId.StandardName := 'Server';
  MonitoredItemArguments.MonitoringParameters := MonitoringParameters;
  //MonitoredItemArguments.SubscriptionParameters.PublishingInterval := 0;
  MonitoredItemArguments.AttributeId := UAAttributeId_EventNotifier;

  Arguments := VarArrayCreate([0, 0], varVariant);
  Arguments[0] := MonitoredItemArguments;

  Client.SubscribeMultipleMonitoredItems(Arguments);

  WriteLn('Processing event notifications for 30 seconds...');
  PumpSleep(30*1000);

  WriteLn('Unsubscribing...');
  Client.UnsubscribeAllMonitoredItems;

  WriteLn('Waiting for 5 seconds...');
  Sleep(5*1000);

  WriteLn('Finished.');
  VarClear(Arguments);
  FreeAndNil(Client);
  FreeAndNil(ClientEventHandlers);
end;


class function THelperMethods10.ObjectTypeIds_BaseEventType: _UANodeId;
  var NodeId: _UANodeId;
  begin
    NodeId := CoUANodeId.Create;
    NodeId.StandardName := 'BaseEventType';
    Result := NodeId;
  end;

class function THelperMethods10.UAFilterElements_SimpleAttribute(TypeId: _UANodeId; simpleRelativeBrowsePathString: string): _UASimpleAttributeOperand;
var
  BrowsePathParser: _UABrowsePathParser;
  Operand: _UASimpleAttributeOperand;
begin
  BrowsePathParser := CoUABrowsePathParser.Create;
  Operand := CoUASimpleAttributeOperand.Create;
  Operand.TypeId.NodeId := TypeId;
  Operand.QualifiedNames := BrowsePathParser.ParseRelative(simpleRelativeBrowsePathString).ToUAQualifiedNameCollection;
  Result := Operand;
end;

class function THelperMethods10.UABaseEventObject_Operands_EventId: _UASimpleAttributeOperand;
begin
  Result := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/EventId');
end;

class function THelperMethods10.UABaseEventObject_Operands_EventType: _UASimpleAttributeOperand;
begin
  Result := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/EventType');
end;

class function THelperMethods10.UABaseEventObject_Operands_NodeId: _UASimpleAttributeOperand;
var
  Operand: _UASimpleAttributeOperand;
begin
  Operand := CoUASimpleAttributeOperand.Create;
  Operand.TypeId.NodeId.StandardName := 'BaseEventType';
  Operand.AttributeId := UAAttributeId_NodeId;
  Result := Operand;
end;

class function THelperMethods10.UABaseEventObject_Operands_SourceNode: _UASimpleAttributeOperand;
begin
  Result := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/SourceNode');
end;

class function THelperMethods10.UABaseEventObject_Operands_SourceName: _UASimpleAttributeOperand;
begin
  Result := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/SourceName');
end;

class function THelperMethods10.UABaseEventObject_Operands_Time: _UASimpleAttributeOperand;
begin
  Result := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/Time');
end;

class function THelperMethods10.UABaseEventObject_Operands_ReceiveTime: _UASimpleAttributeOperand;
begin
  Result := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/ReceiveTime');
end;

class function THelperMethods10.UABaseEventObject_Operands_LocalTime: _UASimpleAttributeOperand;
begin
  Result := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/LocalTime');
end;

class function THelperMethods10.UABaseEventObject_Operands_Message: _UASimpleAttributeOperand;
begin
  Result := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/Message');
end;

class function THelperMethods10.UABaseEventObject_Operands_Severity: _UASimpleAttributeOperand;
begin
  Result := UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType, '/Severity');
end;

class function THelperMethods10.UABaseEventObject_AllFields: _UAAttributeFieldCollection;
var
  Fields: _UAAttributeFieldCollection;
begin
  Fields := CoUAAttributeFieldCollection.Create;
  Fields.Add(UABaseEventObject_Operands_NodeId.ToUAAttributeField);
  Fields.Add(UABaseEventObject_Operands_EventId.ToUAAttributeField);
  Fields.Add(UABaseEventObject_Operands_EventType.ToUAAttributeField);
  Fields.Add(UABaseEventObject_Operands_SourceNode.ToUAAttributeField);
  Fields.Add(UABaseEventObject_Operands_SourceName.ToUAAttributeField);
  Fields.Add(UABaseEventObject_Operands_Time.ToUAAttributeField);
  Fields.Add(UABaseEventObject_Operands_ReceiveTime.ToUAAttributeField);
  Fields.Add(UABaseEventObject_Operands_LocalTime.ToUAAttributeField);
  Fields.Add(UABaseEventObject_Operands_Message.ToUAAttributeField);
  Fields.Add(UABaseEventObject_Operands_Severity.ToUAAttributeField);

  Result := Fields;
end;
// This example shows how to specify criteria for event notifications.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

const UAAttributeId_NodeId = 1;
const UAAttributeId_EventNotifier = 12;

const UAFilterOperator_Equals = 1;
const UAFilterOperator_GreaterThanOrEqual = 5;
const UAFilterOperator_Or = 12;

const UAObjectIds_Server = 'nsu=http://opcfoundation.org/UA/;i=2253';

class ClientEvents {
    function EventNotification($Sender, $E)
    {
        // Display the event
        printf("%s\n", $E);
    }
}

$EndpointDescriptor = "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer";

// Instantiate the client object and hook events
$Client = new COM("OpcLabs.EasyOpc.UA.EasyUAClient");
$ClientEvents = new ClientEvents();
com_event_sink($Client, $ClientEvents, "DEasyUAClientEvents");

$WhereClause = new COM("OpcLabs.EasyOpc.UA.Filtering.UAContentFilterElement");

// Either the severity is >= 500, or the event comes from a specified source node
$Operand1 = UABaseEventObject_Operands_Severity();
$Operand2 = new COM("OpcLabs.EasyOpc.UA.Filtering.UALiteralOperand");
$Operand2->Value = 500;
$Element1 = new COM("OpcLabs.EasyOpc.UA.Filtering.UAContentFilterElement");
$Element1->FilterOperator = UAFilterOperator_GreaterThanOrEqual;
$Element1->FilterOperands->Add($Operand1);
$Element1->FilterOperands->Add($Operand2);
$Operand3 = UABaseEventObject_Operands_SourceNode();
$SourceNodeId = new COM("OpcLabs.EasyOpc.UA.AddressSpace.UANodeId");
$SourceNodeId->ExpandedText = "nsu=http://opcfoundation.org/Quickstarts/AlarmCondition;ns=2;s=1:Metals/SouthMotor";
$Operand4 = new COM("OpcLabs.EasyOpc.UA.Filtering.UALiteralOperand");
$Operand4->Value = $SourceNodeId;
$Element2 = new COM("OpcLabs.EasyOpc.UA.Filtering.UAContentFilterElement");
$Element2->FilterOperator = UAFilterOperator_Equals;
$Element2->FilterOperands->Add($Operand3);
$Element2->FilterOperands->Add($Operand4);
$WhereClause->FilterOperator = UAFilterOperator_Or;
$WhereClause->FilterOperands->Add($Element1);
$WhereClause->FilterOperands->Add($Element2);

$EventFilter = new COM("OpcLabs.EasyOpc.UA.UAEventFilter");
$EventFilter->SelectClauses = UABaseEventObject_AllFields();
$EventFilter->WhereClause = $WhereClause;

$MonitoringParameters = new COM("OpcLabs.EasyOpc.UA.UAMonitoringParameters");
$MonitoringParameters->SamplingInterval = 1000;
$MonitoringParameters->EventFilter = $EventFilter;
$MonitoringParameters->QueueSize = 1000;

$MonitoredItemArguments = new COM("OpcLabs.EasyOpc.UA.OperationModel.EasyUAMonitoredItemArguments");
$MonitoredItemArguments->EndpointDescriptor->UrlString = $EndpointDescriptor;
$MonitoredItemArguments->NodeDescriptor->NodeId->StandardName = "Server";
$MonitoredItemArguments->MonitoringParameters = $MonitoringParameters;
$MonitoredItemArguments->SubscriptionParameters->PublishingInterval = 0;
$MonitoredItemArguments->AttributeId = UAAttributeId_EventNotifier;

$arguments[0] = $MonitoredItemArguments;

printf("Subscribing...\n");
$Client->SubscribeMultipleMonitoredItems($arguments);

printf("Processing monitored item changed events for 30 seconds...\n");
$startTime = time(); do { com_message_pump(1000); } while (time() < $startTime + 30);

printf("Unsubscribing...\n");
$Client->UnsubscribeAllMonitoredItems;

printf("Waiting for 5 seconds...\n");
$startTime = time(); do { com_message_pump(1000); } while (time() < $startTime + 5);


function ObjectTypeIds_BaseEventType() {
    $NodeId = new COM("OpcLabs.EasyOpc.UA.AddressSpace.UANodeId");
    $NodeId->StandardName = "BaseEventType";
    return $NodeId;
}

function UAFilterElements_SimpleAttribute($TypeId, $simpleRelativeBrowsePathString) {
  $BrowsePathParser = new COM("OpcLabs.EasyOpc.UA.Navigation.Parsing.UABrowsePathParser");
  $Operand = new COM("OpcLabs.EasyOpc.UA.Filtering.UASimpleAttributeOperand");
  $Operand->TypeId->NodeId = $TypeId;
  $Operand->QualifiedNames = $BrowsePathParser->ParseRelative($simpleRelativeBrowsePathString)->ToUAQualifiedNameCollection;
  return $Operand;
}

function UABaseEventObject_Operands_NodeId() {
    $Operand = new COM("OpcLabs.EasyOpc.UA.Filtering.UASimpleAttributeOperand");
    $Operand->TypeId->NodeId->StandardName = "BaseEventType";
    $Operand->AttributeId = UAAttributeId_NodeId;
    return $Operand;
}

function UABaseEventObject_Operands_EventId() {
  return UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType(), "/EventId");
}

function UABaseEventObject_Operands_EventType() {
  return UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType(), "/EventType");
}

function UABaseEventObject_Operands_SourceNode() {
  return UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType(), "/SourceNode");
}

function UABaseEventObject_Operands_SourceName() {
  return UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType(), "/SourceName");
}

function UABaseEventObject_Operands_Time() {
  return UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType(), "/Time");
}

function UABaseEventObject_Operands_ReceiveTime() {
  return UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType(), "/ReceiveTime");
}

function UABaseEventObject_Operands_LocalTime() {
  return UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType(), "/LocalTime");
}

function UABaseEventObject_Operands_Message() {
  return UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType(), "/Message");
}

function UABaseEventObject_Operands_Severity() {
  return UAFilterElements_SimpleAttribute(ObjectTypeIds_BaseEventType(), "/Severity");
}

function UABaseEventObject_AllFields() {
    $Fields = new COM("OpcLabs.EasyOpc.UA.UAAttributeFieldCollection");
    $Fields->Add(UABaseEventObject_Operands_NodeId()->ToUAAttributeField);
    $Fields->Add(UABaseEventObject_Operands_EventId()->ToUAAttributeField);
    $Fields->Add(UABaseEventObject_Operands_EventType()->ToUAAttributeField);
    $Fields->Add(UABaseEventObject_Operands_SourceNode()->ToUAAttributeField);
    $Fields->Add(UABaseEventObject_Operands_SourceName()->ToUAAttributeField);
    $Fields->Add(UABaseEventObject_Operands_Time()->ToUAAttributeField);
    $Fields->Add(UABaseEventObject_Operands_ReceiveTime()->ToUAAttributeField);
    $Fields->Add(UABaseEventObject_Operands_LocalTime()->ToUAAttributeField);
    $Fields->Add(UABaseEventObject_Operands_Message()->ToUAAttributeField);
    $Fields->Add(UABaseEventObject_Operands_Severity()->ToUAAttributeField);

    return $Fields;
}
Requirements

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2016, Windows Server 2022; .NET: Linux, macOS, Microsoft Windows

See Also