OPC Studio User's Guide and Reference
UAFilterOperator Enumeration
Example Example 



OpcLabs.EasyOpcUA Assembly > OpcLabs.EasyOpc.UA.Filtering Namespace : UAFilterOperator Enumeration
Filter operator to be evaluated.
Syntax
'Declaration
 

<ComVisibleAttribute(True)>
<DisplayName2Attribute("OPC-UA Filter Operator")>
<GuidAttribute("8095F877-5AE6-4E17-99C1-9951A6FA90E0")>
Public Enum UAFilterOperator 
   Inherits System.Enum
   Implements System.IComparable, System.IConvertible, System.IFormattable 
'Usage
 

Dim instance As UAFilterOperator
[ComVisible(true)]
[DisplayName2("OPC-UA Filter Operator")]
[Guid("8095F877-5AE6-4E17-99C1-9951A6FA90E0")]
public enum UAFilterOperator : System.Enum, System.IComparable, System.IConvertible, System.IFormattable  
[ComVisible(true)]
[DisplayName2("OPC-UA Filter Operator")]
[Guid("8095F877-5AE6-4E17-99C1-9951A6FA90E0")]
public enum class UAFilterOperator : public System.Enum, System.IComparable, System.IConvertible, System.IFormattable
Members
MemberValueDescription
And11TRUE if operand[0] and operand[1] are TRUE.

Remarks:

The following restrictions apply to the operands:
[0]: Any operand that resolves to a Boolean.
[1]: Any operand that resolves to a Boolean.
If any operand cannot be resolved to a Boolean it is considered a NULL.

Between9TRUE if operand[0] is greater or equal to operand[1] and less than or equal to operand[2].

Remarks:

The following restrictions apply to the operands:
[0]: Any operand that resolves to an ordered value.
[1]: Any operand that resolves to an ordered value.
[2]: Any operand that resolves to an ordered value.
If the operands are of different types, the system shall perform any implicit conversion to match all operands to a common type. If no implicit conversion is available and the operands are of different types, the particular result is FALSE.

BitwiseAnd17The result is an integer which matches the size of the largest operand and contains a bitwise And operation of the two operands where both have been converted to the same size (largest of the two operands).

Remarks:

The following restrictions apply to the operands:
[0]: Any operand that resolves to an integer.
[1]: Any operand that resolves to an integer.
If any operand cannot be resolved to an integer it is considered a NULL.

BitwiseOr18The result is an integer which matches the size of the largest operand and contains a bitwise Or operation of the two operands where both have been converted to the same size (largest of the two operands).

Remarks:

The following restrictions apply to the operands:
[0]: Any operand that resolves to an integer.
[1]: Any operand that resolves to an integer.
If any operand cannot be resolved to an integer it is considered a NULL.

Cast13Converts operand[0] to a value with a data type with a NodeId identified by operand[1].

Remarks:

The following restrictions apply to the operands:
[0]: Any operand.
[1]: Any operand that resolves to a NodeId or ExpandedNodeId where the Node is of the NodeClass DataType.
If there is any error in conversion or in any of the parameters then the Cast Operation evaluates to a NULL.

Equals1TRUE if operand[0] is equal to operand[1].

Remarks:

If the operands are of different types, the system shall perform any implicit conversion to a common type. This operator resolves to FALSE if no implicit conversion is available and the operands are of different types. This operator returns FALSE if the implicit conversion fails.

GreaterThan3TRUE if operand[0] is greater than operand[1].

Remarks:

The following restrictions apply to the operands:
[0]: Any operand that resolves to an ordered value.
[1]: Any operand that resolves to an ordered value.
The same conversion rules as defined for Equals apply.

GreaterThanOrEqual5TRUE if operand[0] is greater than or equal to operand[1].

Remarks:

The same conversion rules and restrictions as defined for GreaterThan apply.

InList10TRUE if operand[0] is equal to one or more of the remaining operands.

Remarks:

The Equals Operator is evaluated for operand[0] and each remaining operand in the list. If any Equals evaluation is TRUE, InList returns TRUE.

InView14TRUE if the target Node is contained in the View defined by operand[0].

Remarks:

The following restrictions apply to the operands:
[0]: Any operand that resolves to a NodeId that identifies a View Node.
If operand[0] does not resolve to a NodeId that identifies a View Node, this operation shall always be False.

IsNull2TRUE if operand[0] is a null value.
LessThan4TRUE if operand[0] is less than operand[1].

Remarks:

The same conversion rules and restrictions as defined for GreaterThan apply.

LessThanOrEqual6TRUE if operand[0] is less than or equal to operand[1].

Remarks:

The same conversion rules and restrictions as defined for GreaterThan apply.

Like7TRUE if operand[0] matches a pattern defined by operand[1].

Remarks:

The following restrictions apply to the operands:
[0]: Any operand that resolves to a String.
[1]: Any operand that resolves to a String.
This operator resolves to FALSE if no operand can be resolved to a string.

None0No operator.

Remarks:

This value cannot be actually passed to the server.

Not8TRUE if operand[0] is FALSE.

Remarks:

The following restrictions apply to the operands:
[0]: Any operand that resolves to a Boolean.
If the operand cannot be resolved to a Boolean, the result is a NULL.

OfType15TRUE if the target Node is of type operand[0] or of a subtype of operand[0].

Remarks:

The following restrictions apply to the operands:
[0]: Any operand that resolves to a NodeId that identifies an ObjectType or VariableType Node.
If operand[0]oes not resolve to a NodeId that identifies an ObjectType or VariableType Node, this operation shall always be False.

Or12TRUE if operand[0] or operand[1] are TRUE.

Remarks:

The following restrictions apply to the operands:
[0]: Any operand that resolves to a Boolean.
[1]: Any operand that resolves to a Boolean.
If any operand cannot be resolved to a Boolean it is considered a NULL.

RelatedTo16TRUE if the target Node is of type Operand[0] and is related to a NodeId of the type defined in Operand[1] by the Reference type defined in Operand[2].

Remarks:

Operand[0] or Operand[1] can also point to an element Reference where the referred to element is another RelatedTo operator. This allows chaining of relationships (e.g. A is related to B is related to C), where the relationship is defined by the ReferenceType defined in Operand[2]. In this case, the referred to element returns a list of NodeIds instead of TRUE or FALSE. In this case if any errors occur or any of the operands cannot be resolved to an appropriate value, the result of the chained relationship is an empty list of nodes.
Operand[3] defines the number of hops for which the relationship should be followed. If Operand[3] is 1, then objects shall be directly related. If a hop is greater than 1, then a NodeId of the type described in Operand[1] is checked for at the depth specified by the hop. In this case, the type of the intermediate Node is undefined, and only the Reference type used to reach the end Node is defined. If the requested number of hops cannot be followed, then the result is FALSE, i.e., an empty Node list. If Operand[3] is 0, the relationship is followed to its logical end in a forward direction and each Node is checked to be of the type specified in Operand[1]. If any Node satisfies this criterion, then the result is TRUE, i.e., the NodeId is included in the sub-list.
Operand [4] defines if Operands [0] and [1] should include support for subtypes of the types defined by these operands. A TRUE indicates support for subtypes.
Operand [5] defines if Operand [2] should include support for subtypes of the reference type. A TRUE indicates support for subtypes.

The following restrictions apply to the operands:
[0]: Any operand that resolves to a NodeId or ExpandedNodeId that identifies an ObjectType or VariableType Node or a reference to another element which is a RelatedTo operator.
[1]: Any operand that resolves to a NodeId or ExpandedNodeId that identifies an ObjectType or VariableType Node or a reference to another element which is a RelatedTo operator.
[2]: Any operand that resolves to a NodeId that identifies a ReferenceType Node.
[3]: Any operand that resolves to a value implicitly convertible to Uint32.
[4]: Any operand that resolves to a value implicitly convertible to a boolean; if this operand does not resolve to a Boolean, then a value of FALSE is used.
[5]: Any operand that resolves to a value implicitly convertible to a boolean; if this operand does not resolve to a Boolean, then a value of FALSE is used.
If none of the operands [0], [1], [2], [3] resolves to an appropriate value then the result of this operation shall always be False (or an Empty set in the case of a nested RelatedTo operand).

Remarks

 

General

The Where clause contains the criteria limiting the notifications that the OPC UA server sends - and the OPC UA client receives. The Where clause in OPC UA is similar to the WHERE clause in SQL queries, with the difference that ity operates on events and not on table rows: It is a filter that allows you to choose the events of interest, out of all events provided by the chosen notifier node in the OPC UA server. The OPC UA server itself controls which events are generated by the notifier (for particular types of events, this may be prescribed by OPC UA specifications or other standards). For example, the event might be triggered by a process value exceeding specific limit. In OPC UA, there is no generic way to influence which events get internally generated in the OPC UA server; but the Where clause allows you to pick the events that are of interest to your application.

Obviously, you can also do event filtering on the client side (in your application), and throw away the events that you do not need. But this aproach requires all these events be transferred from the server to the client, which represents a load on all parts involved (server, network, client). Not all filtering criteria can be specified using the Where clause, but whenever you can, you should use it, because the filtering then occurs in the OPC UA server and close to the source, which greatly reduces the load on other parts of the system.

Coding

The Where clause of the event filter is represented using the UAContentFilterElement object. This objects contains the filter operand to be evaluated (the FilterOperator property, which is a UAFilterOperator enumeration), and the operands used by the selected operator (the FilterOperands property, which is a UAFilterOperandCollection). The UAFilterOperator enumeration contains all operators supported by OPC UA (Equals, IsNull, GreaterThan, LessThan, GreaterThanOrEqual, LessThanOrEqual, Like, Not, Between, InList, And, Or, Cast, InView, OfType, RelatedTo, BitwiseAnd, BitwiseOr). The UAFilterOperandCollection is a collection of content filter operands (UAFilterOperand).

The UAFilterOperand is a base class for four different types of filter operands: UAAttributeOperand (an operand consisting of an attribute of a node in a type, with optional relative path and alias), UAContentFilterElement (essentially, an operator with operands), UALiteralOperand (an operand consisting of a literal value), or UASimpleAttributeOperand (an operand consisting of an attribute of a node in a type, with optional simple relative path, and no alias).

In order to make the creation of Where clauses appear shorter in the code, a UAContentFilterElementBuilder class is provided. Instances of this builder can be implicitly converted to the content filter element itself (hence you can create just the UAContentFilterElementBuilder objects, and use them at all places where the UAContentFilterElement object is expected). The builder contains an operator and is a collection of operands; you can use the C# collection initializer to specify the operands.

For further simplification of the coding, the UAFilterElements static class provides an easy way to construct basic filter elements (literal, attribute, or a simple attribute), and elements with various operators. Using the UAFilterElements class is for most cases the recommended way to create the Where clause of the event filter. For example, UAFilterElements.GreaterThanOrEqual creates a Where clause with the ‘>=’ operator. There are methods for each of the OPC UA operators, with various overloads. The UAFilterElements.Attribute, UAFilterElements.Literal and UAFilterElements.SimpleAttribute methods can be used to create other types of filter elements. Moreover, useful overloads exist that assure that you can actually use .NET objects directly as values of operands, and they will be interpreted as literal elements. With use of all these code simplifying features, you can write, for example, the following Where clause:

UAFilterElements.GreaterThanOrEqual(UABaseEventObject.Operands.Severity, 500).

Example 

.NET

// 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 .

Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.AddressSpace
Imports OpcLabs.EasyOpc.UA.AddressSpace.Standard
Imports OpcLabs.EasyOpc.UA.AlarmsAndConditions
Imports OpcLabs.EasyOpc.UA.Filtering
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace AlarmsAndConditions
    Friend Class WhereClause
        Public Shared Sub Main1()
            ' Instantiate the client object and hook events
            Dim client = New EasyUAClient()
            AddHandler client.EventNotification, AddressOf client_EventNotification

            Console.WriteLine("Subscribing...")
            ' Either the severity is >= 500, or the event comes from a specified source node
            client.SubscribeEvent( _
                "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer", _
                UAObjectIds.Server, _
                1000, _
                New UAEventFilterBuilder( _
                    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...")
            Threading.Thread.Sleep(30 * 1000)

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

            Console.WriteLine("Waiting for 5 seconds...")
            Threading.Thread.Sleep(5 * 1000)
        End Sub

        Private Shared Sub client_EventNotification(ByVal sender As Object, ByVal e As EasyUAEventNotificationEventArgs)
            ' Display the event
            Console.WriteLine(e)
        End Sub
    End Class
End Namespace

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 .

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;
}

// 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;

 

 

 

Example

.NET

// 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 .

Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.AddressSpace
Imports OpcLabs.EasyOpc.UA.AddressSpace.Standard
Imports OpcLabs.EasyOpc.UA.AlarmsAndConditions
Imports OpcLabs.EasyOpc.UA.Filtering
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace AlarmsAndConditions
    Friend Class WhereClause
        Public Shared Sub Main1()
            ' Instantiate the client object and hook events
            Dim client = New EasyUAClient()
            AddHandler client.EventNotification, AddressOf client_EventNotification

            Console.WriteLine("Subscribing...")
            ' Either the severity is >= 500, or the event comes from a specified source node
            client.SubscribeEvent( _
                "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer", _
                UAObjectIds.Server, _
                1000, _
                New UAEventFilterBuilder( _
                    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...")
            Threading.Thread.Sleep(30 * 1000)

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

            Console.WriteLine("Waiting for 5 seconds...")
            Threading.Thread.Sleep(5 * 1000)
        End Sub

        Private Shared Sub client_EventNotification(ByVal sender As Object, ByVal e As EasyUAEventNotificationEventArgs)
            ' Display the event
            Console.WriteLine(e)
        End Sub
    End Class
End Namespace
Inheritance Hierarchy

System.Object
   System.ValueType
      System.Enum
         OpcLabs.EasyOpc.UA.Filtering.UAFilterOperator

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

Reference

OpcLabs.EasyOpc.UA.Filtering Namespace

 

 

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