OPC Studio User's Guide and Reference
Examples - OPC Data Access - Read multiple items
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Example 1 (four items at once)

.NET

// This example shows how to read 4 items at once, and display their values, timestamps and qualities.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in C# on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-CSharp .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.

using System;
using System.Diagnostics;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class ReadMultipleItems
    {
        public static void Main1()
        {
            // Instantiate the client object.
            var client = new EasyDAClient();

            DAVtqResult[] vtqResults = client.ReadMultipleItems("OPCLabs.KitServer.2",
                new DAItemDescriptor[]
                    {
                        "Simulation.Random", "Trends.Ramp (1 min)", "Trends.Sine (1 min)", "Simulation.Register_I4"
                    });

            for (int i = 0; i < vtqResults.Length; i++)
            {
                Debug.Assert(vtqResults[i] != null);

                if (vtqResults[i].Succeeded)
                    Console.WriteLine("vtqResults[{0}].Vtq: {1}", i, vtqResults[i].Vtq);
                else
                    Console.WriteLine("vtqResults[{0}] *** Failure: {1}", i, vtqResults[i].ErrorMessageBrief);
            }
        }
    }
}

COM

// This example shows how to read 4 items at once, and display their values, timestamps and qualities.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in PHP on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-PHP .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.

$ReadItemArguments1 = new COM("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments");
$ReadItemArguments1->ServerDescriptor->ServerClass = "OPCLabs.KitServer.2";
$ReadItemArguments1->ItemDescriptor->ItemID = "Simulation.Random";

$ReadItemArguments2 = new COM("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments");
$ReadItemArguments2->ServerDescriptor->ServerClass = "OPCLabs.KitServer.2";
$ReadItemArguments2->ItemDescriptor->ItemID = "Trends.Ramp (1 min)";

$ReadItemArguments3 = new COM("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments");
$ReadItemArguments3->ServerDescriptor->ServerClass = "OPCLabs.KitServer.2";
$ReadItemArguments3->ItemDescriptor->ItemID = "Trends.Sine (1 min)";

$ReadItemArguments4 = new COM("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments");
$ReadItemArguments4->ServerDescriptor->ServerClass = "OPCLabs.KitServer.2";
$ReadItemArguments4->ItemDescriptor->ItemID = "Simulation.Register_I4";

$arguments[0] = $ReadItemArguments1;
$arguments[1] = $ReadItemArguments2;
$arguments[2] = $ReadItemArguments3;
$arguments[3] = $ReadItemArguments4;

$Client = new COM("OpcLabs.EasyOpc.DataAccess.EasyDAClient");

$results = $Client->ReadMultipleItems($arguments);

for ($i = 0; $i < count($results); $i++)
{
    $VtqResult = $results[$i];
    if ($VtqResult->Succeeded)
        printf("results[d].Vtq.ToString()s\n", $i, $VtqResult->Vtq->ToString);
    else
        printf("results[d]: *** Failures\n", $i, $VtqResult->ErrorMessageBrief);
}

Python

# This example shows how to read 4 items at once, and display their values, timestamps and qualities.
#
# 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 .
# Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
# a commercial license in order to use Online Forums, and we reply to every post.
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc

# Import .NET namespaces.
from OpcLabs.EasyOpc import *
from OpcLabs.EasyOpc.DataAccess import *
from OpcLabs.EasyOpc.DataAccess.OperationModel import *
from OpcLabs.EasyOpc.OperationModel import *


# Instantiate the client object.
client = EasyDAClient()

#
vtqResultArray = client.ReadMultipleItems([
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Simulation.Random')),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Trends.Ramp (1 min)')),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Trends.Sine (1 min)')),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Simulation.Register_I4')),
    ])

for i, vtqResult in enumerate(vtqResultArray):
    assert vtqResult is not None
    if vtqResult.Succeeded:
        print('vtqResultArray[', i, '].Vtq: ', vtqResult.Vtq, sep='')
    else:
        print('vtqResultArray[', i, '] *** Failure: ', vtqResult.ErrorMessageBrief, sep='')

Example 2 (many items)

.NET

// This example repeatedly reads a large number of items.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in C# on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-CSharp .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.

using System;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class ReadMultipleItems
    {
        private const int RepeatCount = 10;
        private const int NumberOfItems = 1000;

        public static void ManyRepeat()
        {
            Console.WriteLine("Creating array of arguments...");
            var arguments = new DAReadItemArguments[NumberOfItems];
            for (int i = 0; i < NumberOfItems; i++)
            {
                int copy = (i / 100) + 1;
                int phase = i % 100;
                string itemId = FormattableString.Invariant($"Simulation.Incrementing.Copy_{copy}.Phase_{phase}");
                Console.WriteLine(itemId);

                var readItemArguments = new DAReadItemArguments("OPCLabs.KitServer.2", itemId);
                arguments[i] = readItemArguments;
            }

            // Instantiate the client object.
            var client = new EasyDAClient();

            for (int iRepeat = 1; iRepeat <= RepeatCount; iRepeat++)
            {
                Console.WriteLine("Reading items...");
                DAVtqResult[] vtqResults = client.ReadMultipleItems(arguments);

                int successCount = 0;
                foreach (DAVtqResult vtqResult in vtqResults)
                    if (vtqResult.Succeeded)
                        successCount++;
                Console.WriteLine($"Success count: {successCount}");
            }
        }
    }
}

COM

Rem This example repeatedly reads a large number of items.
Rem
Rem Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
Rem OPC client and subscriber examples in VBScript on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBScript .
Rem Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
Rem a commercial license in order to use Online Forums, and we reply to every post.

Option Explicit

Const repeatCount = 10
Const numberOfItems = 1000

WScript.Echo "Creating array of arguments..."
Dim arguments(): ReDim arguments(numberOfItems - 1)
Dim i: For i = 0 To numberOfItems - 1
    Dim copy: copy = Int(i / 100) + 1
    Dim phase: phase = i Mod 100
    Dim itemId: itemId = "Simulation.Incrementing.Copy_" & copy & ".Phase_" & phase
    WScript.Echo itemId

    Dim ReadItemArguments: Set ReadItemArguments = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
    ReadItemArguments.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
    ReadItemArguments.ItemDescriptor.ItemID = itemId

    Set arguments(i) = ReadItemArguments
Next

Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")

Dim iRepeat: For iRepeat = 1 To repeatCount
    WScript.Echo "Reading items..."
    Dim results: results = Client.ReadMultipleItems(arguments)

    Dim successCount: successCount = 0
    For i = LBound(results) To UBound(results)
        Dim VtqResult: Set VtqResult = results(i)
        If VtqResult.Succeeded Then successCount = successCount + 1
    Next
    WScript.Echo "Success count: " & successCount
Next

Python

# This example repeatedly reads a large number of items.
#
# 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 .
# Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
# a commercial license in order to use Online Forums, and we reply to every post.
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc

# Import .NET namespaces.
from OpcLabs.EasyOpc import *
from OpcLabs.EasyOpc.DataAccess import *
from OpcLabs.EasyOpc.DataAccess.OperationModel import *
from OpcLabs.EasyOpc.OperationModel import *


REPEAT_COUNT = 10
NUMBER_OF_ITEMS = 1000

print('Creating array of arguments...')
argumentArray = [None]*NUMBER_OF_ITEMS
for i in range(NUMBER_OF_ITEMS):
    copy = (i//100) + 1
    phase = i % 100
    itemId = 'Simulation.Incrementing.Copy_{}.Phase_{}'.format(copy, phase)
    print(itemId)
    #
    readItemArguments = DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor(itemId))
    argumentArray[i] = readItemArguments

# Instantiate the client object.
client = EasyDAClient()

#
for iRepeat in range(1, REPEAT_COUNT + 1):
    print('Reading items...')
    vtqResultArray = client.ReadMultipleItems(argumentArray)
    #
    successCount = 0
    for vtqResult in vtqResultArray:
        if vtqResult.Succeeded:
            successCount = successCount + 1
        print('Success count: ', successCount, sep='')

print('Finished.')

Example 3 (synchronous read)

.NET

// This example shows how to read 4 items at once synchronously, and display their values, timestamps and qualities.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in C# on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-CSharp .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.

using System;
using System.Diagnostics;
using OpcLabs.EasyOpc.DataAccess;
using OpcLabs.EasyOpc.DataAccess.OperationModel;

namespace DocExamples.DataAccess._EasyDAClient
{
    partial class ReadMultipleItems
    {
        public static void Synchronous()
        {
            // Instantiate the client object.
            var client = new EasyDAClient();

            // Specify that only synchronous method is allowed. By default, both synchronous and asynchronous methods are
            // allowed, and the component picks a suitable method automatically. Disallowing asynchronous method leaves
            // only the synchronous method available for selection.
            client.InstanceParameters.Mode.AllowAsynchronousMethod = false;

            DAVtqResult[] vtqResults = client.ReadMultipleItems("OPCLabs.KitServer.2",
                new DAItemDescriptor[]
                    {
                        "Simulation.Random", "Trends.Ramp (1 min)", "Trends.Sine (1 min)", "Simulation.Register_I4"
                    });

            for (int i = 0; i < vtqResults.Length; i++)
            {
                Debug.Assert(vtqResults[i] != null);

                if (vtqResults[i].Succeeded)
                    Console.WriteLine("vtqResult[{0}].Vtq: {1}", i, vtqResults[i].Vtq);
                else
                    Console.WriteLine("vtqResult[{0}] *** Failure: {1}", i, vtqResults[i].ErrorMessageBrief);
            }
        }

        
        // Example output:
        //
        //vtqResult[0].Vtq: 0.00125125888851588 { System.Double} @2020-04-10T15:29:20.642; GoodNonspecific(192)
        //vtqResult[1].Vtq: 0.344052940607071 {System.Double} @2020-04-10T15:29:20.643; GoodNonspecific(192)
        //vtqResult[2].Vtq: 0.830410616568378 {System.Double} @2020-04-10T15:29:20.643; GoodNonspecific(192)
        //vtqResult[3].Vtq: 0 {System.Int32} @1601-01-01T00:00:00.000; GoodNonspecific(192)
    }
}

COM

Rem This example shows how to read 4 items at once synchronously, and display their values, timestamps and qualities.
Rem
Rem Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
Rem OPC client and subscriber examples in VBScript on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBScript .
Rem Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
Rem a commercial license in order to use Online Forums, and we reply to every post.

Option Explicit

Dim ReadItemArguments1: Set ReadItemArguments1 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments1.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments1.ItemDescriptor.ItemID = "Simulation.Random"

Dim ReadItemArguments2: Set ReadItemArguments2 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments2.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments2.ItemDescriptor.ItemID = "Trends.Ramp (1 min)"

Dim ReadItemArguments3: Set ReadItemArguments3 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments3.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments3.ItemDescriptor.ItemID = "Trends.Sine (1 min)"

Dim ReadItemArguments4: Set ReadItemArguments4 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments4.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments4.ItemDescriptor.ItemID = "Simulation.Register_I4"

Dim arguments(3)
Set arguments(0) = ReadItemArguments1
Set arguments(1) = ReadItemArguments2
Set arguments(2) = ReadItemArguments3
Set arguments(3) = ReadItemArguments4

Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")

' Specify that only synchronous method is allowed. By default, both synchronous and asynchronous methods are allowed, and 
' the component picks a suitable method automatically. Disallowing asynchronous method leaves only the synchronous method
' available for selection.
Client.InstanceParameters.Mode.AllowAsynchronousMethod = False

Dim results: results = Client.ReadMultipleItems(arguments)

Dim i: For i = LBound(results) To UBound(results)
    Dim VtqResult: Set VtqResult = results(i)
    If VtqResult.Succeeded Then
        WScript.Echo "results(" & i & ").Vtq.ToString(): " & VtqResult.Vtq.ToString()
    Else
        WScript.Echo "results(" & i & ") *** Failure: " & VtqResult.ErrorMessageBrief
    End If
Next

Python

# This example shows how to read 4 items at once synchronously, and display their values, timestamps and qualities.
#
# 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 .
# Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
# a commercial license in order to use Online Forums, and we reply to every post.
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc

# Import .NET namespaces.
from OpcLabs.EasyOpc import *
from OpcLabs.EasyOpc.DataAccess import *
from OpcLabs.EasyOpc.DataAccess.OperationModel import *
from OpcLabs.EasyOpc.OperationModel import *


# Instantiate the client object.
client = EasyDAClient()

# Specify that only synchronous method is allowed. By default, both synchronous and asynchronous methods are
# allowed, and the component picks a suitable method automatically. Disallowing asynchronous method leaves
# only the synchronous method available for selection.
client.InstanceParameters.Mode.AllowAsynchronousMethod = False

#
vtqResultArray = client.ReadMultipleItems([
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Simulation.Random')),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Trends.Ramp (1 min)')),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Trends.Sine (1 min)')),
    DAReadItemArguments(ServerDescriptor('OPCLabs.KitServer.2'), DAItemDescriptor('Simulation.Register_I4')),
    ])

for i, vtqResult in enumerate(vtqResultArray):
    assert vtqResult is not None
    if vtqResult.Succeeded:
        print('vtqResultArray[', i, '].Vtq: ', vtqResult.Vtq, sep='')
    else:
        print('vtqResultArray[', i, '] *** Failure: ', vtqResult.ErrorMessageBrief, sep='')

Example 4 (test success)

COM

Rem This example shows how to read 2 items (first valid, second invalid), test for success of each read and display either 
Rem the DAVtq or the Exception.
Rem
Rem Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
Rem OPC client and subscriber examples in VBScript on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBScript .
Rem Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
Rem a commercial license in order to use Online Forums, and we reply to every post.

Option Explicit

Dim ReadItemArguments1: Set ReadItemArguments1 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments1.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments1.ItemDescriptor.ItemID = "Simulation.Random"

Dim ReadItemArguments2: Set ReadItemArguments2 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments2.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments2.ItemDescriptor.ItemID = "UnknownItem"

Dim arguments(1)
Set arguments(0) = ReadItemArguments1
Set arguments(1) = ReadItemArguments2

Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")
Dim results: results = Client.ReadMultipleItems(arguments)

Dim i: For i = LBound(results) To UBound(results)
    Dim VtqResult: Set VtqResult = results(i)
    If VtqResult.Succeeded Then
        WScript.Echo "results(" & i & ").Vtq.ToString(): " & VtqResult.Vtq.ToString()
    Else
        WScript.Echo "results(" & i & ") *** Failure: " & VtqResult.ErrorMessageBrief
    End If
Next

Example 5 (usage error upon failure)

Rem This example attempts to read 3 items (first valid, second invalid, third valid again), and display their values, 
Rem timestamps and qualities. Without testing for a success, a run-time error occurs when accessing the Vtq property
Rem of a failed result.
Rem
Rem Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
Rem OPC client and subscriber examples in VBScript on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBScript .
Rem Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
Rem a commercial license in order to use Online Forums, and we reply to every post.

Option Explicit

Dim ReadItemArguments1: Set ReadItemArguments1 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments1.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments1.ItemDescriptor.ItemID = "Simulation.Random"

Dim ReadItemArguments2: Set ReadItemArguments2 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments2.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments2.ItemDescriptor.ItemID = "UnknownItem"

Dim ReadItemArguments3: Set ReadItemArguments3 = CreateObject("OpcLabs.EasyOpc.DataAccess.OperationModel.DAReadItemArguments")
ReadItemArguments3.ServerDescriptor.ServerClass = "OPCLabs.KitServer.2"
ReadItemArguments3.ItemDescriptor.ItemID = "Trends.Ramp (1 min)"

Dim arguments(2)
Set arguments(0) = ReadItemArguments1
Set arguments(1) = ReadItemArguments2
Set arguments(2) = ReadItemArguments3

Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")
Dim results: results = Client.ReadMultipleItems(arguments)

Dim i: For i = LBound(results) To UBound(results)
    ' This is an anti-example - you should not access the Vtq property without testing the success first!
    WScript.Echo "results(" & i & ").Vtq.ToString(): " & results(i).Vtq.ToString()
Next
See Also
Examples - OPC Data Access - Read multiple item values
Examples - OPC Data Access - Read a single item
Examples - OPC Data Access - Subscribe to multiple items
Examples - OPC Data Access - Read multiple items and measure time
Examples - OPC Data Access - Read items from the device
Examples - OPC Data Access - Read while subscribed

Concepts

Reading from OPC Classic Items

Examples - Client OPC Unified Architecture

Examples - OPC Unified Architecture - Read multiple nodes or attributes

 

 

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