OPC Studio User's Guide and Reference
Examples - OPC Unified Architecture - Read values from two servers

.NET

// This example shows that either a single client object, or multiple client objects can be used to read values from two
// servers.
//
// 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.UA;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples._EasyUAClient
{
    partial class ReadValue
    {
        public static void MultipleServers()
        {
            // Define which servers we will work with.
            UAEndpointDescriptor endpointDescriptor1 =
                "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
            // or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            // or "https://opcua.demo-this.com:51212/UA/SampleServer/"
            UAEndpointDescriptor endpointDescriptor2 =
                "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer";



            // Part 1: Use a single client object.
            // This demonstrates the fact that the client objects do *not* represent connections to individual servers.
            // Instead, they are able to maintain connections to multiple servers internally. API method calls on the client
            // object include the server's endpoint descriptor in their arguments, so you can specify a different endpoint
            // with each operation.
            Console.WriteLine();

            // Instantiate the client object
            var client = new EasyUAClient();

            Console.WriteLine("Obtaining values of nodes using a single client object...");
            object value1, value2;
            try
            {
                // The node Id we are reading returns the product name of the server.
                value1 = client.ReadValue(endpointDescriptor1, "nsu=http://opcfoundation.org/UA/ ;i=2261");
                value2 = client.ReadValue(endpointDescriptor2, "nsu=http://opcfoundation.org/UA/ ;i=2261");
                // Note: For efficiency (reading from the two servers in parallel), it would be better to use the
                // ReadMultipleValues method here, but this example is made for code clarity.
            }
            catch (UAException uaException)
            {
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message);
                return;
            }

            // Display results
            Console.WriteLine("value1: {0}", value1);
            Console.WriteLine("value2: {0}", value2);



            // Part 2: Use multiple client objects.
            // This demonstrates the fact that it is also possible to use multiple client objects, and on the OPC side, the
            // behavior will be the same as if you had used a single client object. Multiple client objects consume somewhat
            // more resources on the client side, but they come handy if, for example,
            // - you cannot easily pass around the single pre-created client object to various parts in your code, or
            // - you are using subscriptions, and you want to hook separate event handlers for different purposes, or
            // - you need to set something in the instance parameters of the client object differently for different
            // connections.
            Console.WriteLine();

            // Instantiate the client objects.
            var client1 = new EasyUAClient();
            var client2 = new EasyUAClient();

            Console.WriteLine("Obtaining values of nodes using multiple client objects...");
            try
            {
                // The node Id we are reading returns the product name of the server.
                value1 = client1.ReadValue(endpointDescriptor1, "nsu=http://opcfoundation.org/UA/ ;i=2261");
                value2 = client2.ReadValue(endpointDescriptor2, "nsu=http://opcfoundation.org/UA/ ;i=2261");
            }
            catch (UAException uaException)
            {
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message);
                return;
            }

            // Display results
            Console.WriteLine("value1: {0}", value1);
            Console.WriteLine("value2: {0}", value2);



            // Example output:
            //
            //Obtaining values of nodes using a single client object...
            //value1: OPC UA SDK Samples
            //value2: OPC UA Workshop Samples
            //
            //Obtaining values of nodes using multiple client objects...
            //value1: OPC UA SDK Samples
            //value2: OPC UA Workshop Samples
        }
    }
}
' This example shows that either a single client object, or multiple client objects can be used to read values from two
' servers.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
' OPC client and subscriber examples in VB.NET on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBNET .
' 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.

Imports Newtonsoft.Json.Linq
Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace _EasyUAClient
    Partial Friend Class ReadValue
        Public Shared Sub MultipleServers()

            ' Define which server we will work with.
            Dim endpointDescriptor1 As UAEndpointDescriptor =
                    "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
            ' or "http://opcua.demo-this.com:51211/UA/SampleServer" (currently not supported)
            ' or "https://opcua.demo-this.com:51212/UA/SampleServer/"
            Dim endpointDescriptor2 As UAEndpointDescriptor =
                    "opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer"


            ' Part 1: Use a single client object.
            ' This demonstrates the fact that the client objects do *not* represent connections to individual servers.
            ' Instead, they are able to maintain connections to multiple servers internally. API method calls on the client
            ' object include the server's endpoint descriptor in their arguments, so you can specify a different endpoint
            ' with each operation.
            Console.WriteLine()

            ' Instantiate the client object
            Dim client = New EasyUAClient()

            Console.WriteLine("Obtaining values of nodes using a single client object...")
            ' Obtain value of a node
            Dim value1 As Object
            Dim value2 As Object
            Try
                ' The node Id we are reading returns the product name of the server.
                value1 = client.ReadValue(endpointDescriptor1, "nsu=http://opcfoundation.org/UA/ ;i=2261")
                value2 = client.ReadValue(endpointDescriptor2, "nsu=http://opcfoundation.org/UA/ ;i=2261")
                ' Note: For efficiency(reading from the two servers in parallel), it would be better to use the
                ' ReadMultipleValues method here, but this example is made for code clarity.
            Catch uaException As UAException
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException.Message)
                Exit Sub
            End Try

            ' Display results
            Console.WriteLine("value1: {0}", value1)
            Console.WriteLine("value2: {0}", value2)


            ' Part 2: Use multiple client objects.
            ' This demonstrates the fact that it is also possible to use multiple client objects, and on the OPC side, the
            ' behavior will be the same as if you had used a single client object. Multiple client objects consume somewhat
            ' more resources on the client side, but they come handy if, for example,
            ' - you cannot easily pass around the single pre-created client object to various parts in your code, or
            ' - you are using subscriptions, and you want to hook separate event handlers for different purposes, or
            ' - you need to set something in the instance parameters of the client object differently for different
            ' connections.
            Console.WriteLine()

            ' Instantiate the client objects.
            Dim client1 = New EasyUAClient()
            Dim client2 = New EasyUAClient()

            Console.WriteLine("Obtaining values of nodes using multiple client objects...")
            Try
                ' The node Id we are reading returns the product name of the server.
                value1 = client1.ReadValue(endpointDescriptor1, "nsu=http://opcfoundation.org/UA/ ;i=2261")
                value2 = client2.ReadValue(endpointDescriptor2, "nsu=http://opcfoundation.org/UA/ ;i=2261")
            Catch uaException As UAException
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException.Message)
                Exit Sub
            End Try

            ' Display results
            Console.WriteLine("value1: {0}", value1)
            Console.WriteLine("value2: {0}", value2)


            ' Example output
            '
            'Obtaining values of nodes using a single client object...
            'value1: Opc UA SDK Samples
            'value2: Opc UA Workshop Samples
            '
            'Obtaining values of nodes using multiple client objects...
            'value1: Opc UA SDK Samples
            'value2: Opc UA Workshop Samples
        End Sub
    End Class
End Namespace

Python

# This example shows that either a single client object, or multiple client objects can be used to read values from two
# servers.
#
# 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.UA import *
from OpcLabs.EasyOpc.UA.OperationModel import *


# Define which servers we will work with.
endpointDescriptor1 = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:51210/UA/SampleServer')
# or 'http://opcua.demo-this.com:51211/UA/SampleServer' (currently not supported)
# or 'https://opcua.demo-this.com:51212/UA/SampleServer/'
endpointDescriptor2 = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer')


# Part 1: Use a single client object.
# This demonstrates the fact that the client objects do *not* represent connections to individual servers.
# Instead, they are able to maintain connections to multiple servers internally. API method calls on the client
# object include the server's endpoint descriptor in their arguments, so you can specify a different endpoint
# with each operation.
print()

# Instantiate the client object.
client = EasyUAClient()

print('Obtaining values of nodes using a single client object...')
try:
    # The node Id we are reading returns the product name of the server.
    value1 = IEasyUAClientExtension.ReadValue(client,
                                              endpointDescriptor1,
                                              UANodeDescriptor('nsu=http://opcfoundation.org/UA/ ;i=2261'))
    value2 = IEasyUAClientExtension.ReadValue(client,
                                              endpointDescriptor2,
                                              UANodeDescriptor('nsu=http://opcfoundation.org/UA/ ;i=2261'))
except UAException as uaException:
    print('*** Failure: ' + uaException.GetBaseException().Message)
    exit()

# Display results.
print('value1: ', value1, sep='')
print('value2: ', value2, sep='')


# Part 2: Use multiple client objects.
# This demonstrates the fact that it is also possible to use multiple client objects, and on the OPC side, the
# behavior will be the same as if you had used a single client object. Multiple client objects consume somewhat
# more resources on the client side, but they come handy if, for example,
# - you cannot easily pass around the single pre-created client object to various parts in your code, or
# - you are using subscriptions, and you want to hook separate event handlers for different purposes, or
# - you need to set something in the instance parameters of the client object differently for different
# connections.
print()

# Instantiate the client objects.
client1 = EasyUAClient()
client2 = EasyUAClient()

print('Obtaining values of nodes using multiple client objects...')
try:
    # The node Id we are reading returns the product name of the server.
    value1 = IEasyUAClientExtension.ReadValue(client1,
                                              endpointDescriptor1,
                                              UANodeDescriptor('nsu=http://opcfoundation.org/UA/ ;i=2261'))
    value2 = IEasyUAClientExtension.ReadValue(client2,
                                              endpointDescriptor2,
                                              UANodeDescriptor('nsu=http://opcfoundation.org/UA/ ;i=2261'))
except UAException as uaException:
    print('*** Failure: ' + uaException.GetBaseException().Message)
    exit()

# Display results.
print('value1: ', value1, sep='')
print('value2: ', value2, sep='')


print()
print('Finished.')

 

See Also

Concepts