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Get Data Type methods

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29 Apr 2013 11:44 #1306 by support
Replied by support on topic Get Data Type methods
Hello.

There is now a new build (5.21.175.1) available from the public download area. It contains an optimization for GetMultiplePropertyValues with OPC-DA Version 3.0. I hope it helps.

Best regards

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23 Apr 2013 06:42 #1302 by support
Replied by support on topic Get Data Type methods
Below is an example of the "trick". The efficiency of it depends on factors that are explained in the comments, and you need to consider and measure that. In addition, we will change the implementation of GetMultiplePropertyValues so that it works more efficiently with OPC-DA 3.0 servers. Please allow some time (several days) before the new build is available.
// This example shows how to obtain data types of leaves in the OPC-DA address 
// space by browsing and filtering, i.e. without the use of OPC properties. 
// This technique allows determining the data types with servers that only 
// support OPC-DA 1.0. It can also be more effective than the use of 
// GetMultiplePropertyValues, if there is large number of leaves, and 
// relatively small number of data types to be checked.
 
using System;
using System.Collections.Generic;
using OpcLabs.EasyOpc;
using OpcLabs.EasyOpc.DataAccess;
 
namespace DocExamples
{
    namespace _EasyDAClient
    {
        /*partial*/ class BrowseNodes
        {
            public static void DataTypes()
            {
                var easyDAClient = new EasyDAClient();
 
                // Define the list of data types we will be checking for. 
                // Change as needed for your application.
                // This technique is only usable if there is a known list of 
                // data types you are interested in. If you are interested in 
                // all leaves, even those that are of data types not explicitly 
                // listed, always include VarType.Empty as the first data type. 
                // The leaves of "unlisted" data types will have VarType.Empty 
                // associated with them.
                var dataTypes = new VarType[] { VarType.Empty, VarType.I2, VarType.R4 };
 
                // For each leaf found, this dictionary wil hold its associated data type.
                var dataTypeDictionary = new Dictionary<DANodeElement, VarType>();
 
                // For each data type, browse for leaves of this data type.
                foreach (VarType dataType in dataTypes)
                {
                    var nodeFilter = new DANodeFilter(DABrowseFilter.Leaves, "", "", dataType);
                    DANodeElementCollection nodeElements =
                        easyDAClient.BrowseNodes("", "OPCLabs.KitServer.2", "Greenhouse", nodeFilter);
 
                    // Store the leaf information into the dictionary, and 
                    // associate the current data type with it.
                    foreach (var nodeElement in nodeElements)
                        dataTypeDictionary[nodeElement] = dataType;
                }
 
                // Display each leaf found, and its associated data type.
                foreach (KeyValuePair<DANodeElement, VarType> pair in dataTypeDictionary)
                {
                    DANodeElement nodeElement = pair.Key;
                    VarType dataType = pair.Value;
                    Console.WriteLine("{0}: {1}", nodeElement, dataType);
                }
            }
        }
    }
}

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22 Apr 2013 15:26 #1301 by arahming
Replied by arahming on topic Get Data Type methods
The program was to be designed to collect data from multiple OPC servers some 2.0 and some 3.0 if you have any tricks it would be appreciated otherwise I am going to have to redesign the program

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20 Apr 2013 07:26 #1298 by support
Replied by support on topic Get Data Type methods
No problem if you ask further...

What you say got me thinking, and I have closely examined the code inside. The behavior is as follows:

1) We check if OPC-DA 3.0 is supported by the server. If so, we use the OPC-DA 3.0 interface to obtain the properties. The OPC-DA 3.0 allows properties from multiple items be collected using one call, which should be faster. Unfortunately, it appears that our current implementation still calls it per each item individually. This looks like something that we can fix.

2) If OPC-DA 3.0 is not supported, we use the OPC-DA 2.0 method for obtaining properties. In this case, we HAVE to go item by item, it is dictated by the OPC interface, so no performance gains can be achieved here.

3) If only OPC-DA 1.0 is supported, it is an error, as OPC-DA 1.0 does not have a concept of properties.

It is likely that your code is just fine. What I need to know at this moment is whether the OPC server supports OPC-DA 2.0, OPC-DA 3.0, or both. Can you find this out? Which server is it? Note that we also have this information available from the browsing methods and dialogs.

If you find that OPC-DA 3.0 is supported, we will make a code change inside the component to allow properties for multiple items be truly obtained at once, hoping for better performance, although the precise effect will depend on circumstances.

If you find that OPC-DA 3.0 is not supported, then there is no way to make obtainining the properties faster. As I wrote earlier, they were not intended for fast access, that is an intentional design decision of the OPC spec. But, I am thinking of one possible "trick" that can be tried in this case: If you just need the data type, then you cxan "indirectly" obtain via browsing, specifying a filter for a specific type. This might help if there are just a few specific datatypes that you need to work with. I can elaborate on this idea, but only after we know the OPC-DA specs that are provided by your server.

Best regards

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19 Apr 2013 16:16 #1297 by arahming
Replied by arahming on topic Get Data Type methods
I have attempted over the last week to integrate your solution into my original code and it acctually made things worse. I hate to ask but can I get another example of how my original code would work with this code you produced

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11 Apr 2013 08:05 #1294 by support
Replied by support on topic Get Data Type methods
This exception is from the BrowseNodes call, not from the GetMultiplePropertyValues.
The GetMultiplePropertyValues should work for any node directly.

The exception from browsing is not related to GetMultiplePropertyValues. It has to do with various versions of OPC specifications, and various level of support in OPC Server. The exception text tries to explain the situation:

Change browse position not feasible. This error occurs during browsing, if the OPC Server does not support OPC-DA 2.0 (OPC_BROWSE_TO value of dwBrowseDirection argument in IOPCBrowseServerAddressSpace::ChangeBrowsePosition) and the ItemID to browse into has not been previously encountered during browsing. If the OPC Server supports OPC-DA 2.0, this error means that the ItemID is invalid. If the OPC Server only supports OPC-DA 1.0, this is neither an error of the OPC Server nor the OPC Client, but rather an indication that in order to assure succesful browsing, the application code should start the browsing at the root and proceed gradually to subsequent levels. If the OPC Server only supports OPC-DA 3.0, the error indicates that the application should provide full ItemID instead of (or in addition to) the path sequence of branch ItemIDs.

This is quite lengthy text, in order to explain the complexity properly, but in short, in your case (when the ItemID is correct), it means that
  • The OPC Server you are connecting to does not support really "random" browsing, starting from any node,
  • but you can easily resolve it in your case, because in the original code you sent, you will be making a recursive browsing, starting from the root. This way, any node you browse into will already be a result of the previous call, and in this case, the error won't appear.
Best regards
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10 Apr 2013 17:50 #1293 by arahming
Replied by arahming on topic Get Data Type methods
I have tested it on several servers it works on some but not on others this is the error

OpcLabs.EasyOpc.OpcException was unhandled
Message=OPC operation failure.
Source=OpcLabs.EasyOpcClassicRaw
ErrorCode=-1073442812
StackTrace:
at OpcLabs.EasyOpcRaw.DataAccess.RawEasyDAClient.CheckComResult(CHResult* hResult, IErrorInfo* pErrorInfo)
at OpcLabs.EasyOpcRaw.DataAccess.RawEasyDAClient.CheckComResult(CHResult* hResult)
at OpcLabs.EasyOpcRaw.DataAccess.RawEasyDAClient.BrowseNodes(ServerDescriptor serverDescriptor, NodeDescriptor parentNodeDescriptor, DANodeFilter nodeFilter)
at OpcLabs.EasyOpc.DataAccess.EasyDAClient.BrowseNodes(ServerDescriptor serverDescriptor, DANodeDescriptor parentNodeDescriptor, DANodeFilter nodeFilter)
at OpcLabs.EasyOpc.DataAccess.EasyDAClient.BrowseLeaves(ServerDescriptor serverDescriptor, DANodeDescriptor parentNodeDescriptor, String elementNameFilter, String vendorFilter)
at OpcLabs.EasyOpc.DataAccess.EasyDAClient.BrowseLeaves(ServerDescriptor serverDescriptor, DANodeDescriptor parentNodeDescriptor, String elementNameFilter)
at OpcLabs.EasyOpc.DataAccess.EasyDAClient.BrowseLeaves(ServerDescriptor serverDescriptor, DANodeDescriptor parentNodeDescriptor)
at ConsoleApplication3.Program.Main(String[] args) in F:\Visual Studio\Projects\ConsoleApplication3\ConsoleApplication3\Program.cs:line 20
at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
InnerException: System.Runtime.InteropServices.COMException
Message=Change browse position not feasible. This error occurs during browsing, if the OPC Server does not support OPC-DA 2.0 (OPC_BROWSE_TO value of dwBrowseDirection argument in IOPCBrowseServerAddressSpace::ChangeBrowsePosition) and the ItemID to browse into has not been previously encountered during browsing. If the OPC Server supports OPC-DA 2.0, this error means that the ItemID is invalid. If the OPC Server only supports OPC-DA 1.0, this is neither an error of the OPC Server nor the OPC Client, but rather an indication that in order to assure succesful browsing, the application code should start the browsing at the root and proceed gradually to subsequent levels. If the OPC Server only supports OPC-DA 3.0, the error indicates that the application should provide full ItemID instead of (or in addition to) the path sequence of branch ItemIDs.
Source=OpcLabs.EasyOpcRaw.DataAccess.RawEasyDAClient
ErrorCode=-1073442812
InnerException:

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10 Apr 2013 13:32 #1292 by support
Replied by support on topic Get Data Type methods
Please provide the details of the exception ("crash") you are getting. The code is supposed to work for any branch.

And, which OPC server are you connecting to? Is it a server from Rockwell?

Thank you

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09 Apr 2013 04:54 #1290 by arahming
Replied by arahming on topic Get Data Type methods
I guess I am not fully understanding how this method works if I have a structure like the following

tags.tag1.int
tags.int
tags.float
tags.tag2.int

and use the code below with the parentnodedesc as "Tags" It will return the data typs for tags.int and tags.float but if I set the parentnodedesc as "tags.tag1" the program crashes likewise for "tags.tag2"

I have searched the class library but not finding anyway to go deeper than 1 branch

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06 Apr 2013 13:08 #1288 by support
Replied by support on topic Get Data Type methods
Here is an example - I hope it helps:
// This example shows how to obtain a data type of all OPC items under a branch.
 
using System;
using System.Linq;
using OpcLabs.BaseLib;
using OpcLabs.EasyOpc;
using OpcLabs.EasyOpc.DataAccess;
 
namespace DocExamples
{
    namespace _EasyDAClient
    {
        class GetMultiplePropertyValues
        {
            public static void DataType()
            {
                var easyDAClient = new EasyDAClient();
                ServerDescriptor serverDescriptor = "OPCLabs.KitServer.2";
 
                // Browse for all leaves under the "Simulation" branch
                DANodeElementCollection nodeElementCollection = easyDAClient.BrowseLeaves(serverDescriptor, "Simulation");
 
                // Create list of property descriptors for the DataType property, one for each leaf obtained
                DAPropertyDescriptor[] propertyDescriptorArray = nodeElementCollection
                    .Where(element => !element.IsHint)  // filter out hint leafs that do not represent real OPC items (rare)
                    .Select(element => new DAPropertyDescriptor(element, DAPropertyId.DataType))
                    .ToArray();
 
                // Get the value of DataType property; it is a 16-bit signed integer
                ValueResult[] valueResultArray = easyDAClient.GetMultiplePropertyValues(serverDescriptor, 
                    propertyDescriptorArray);
 
                for (int i = 0; i < valueResultArray.Length; i++)
                {
                    DAPropertyDescriptor propertyDescriptor = propertyDescriptorArray[i];
 
                    // Check if there has been an error getting the property value
                    ValueResult valueResult = valueResultArray[i];
                    if (valueResult.Exception != null)
                    {
                        Console.WriteLine("{0}: *** {1}", propertyDescriptor.ItemId, valueResult.Exception.Message);
                        continue;
                    }
 
                    // Convert the data type to VarType
                    var varType = (VarType)(short)valueResult.Value;
 
                    // Display the obtained data type
                    Console.WriteLine("{0}: {1}", propertyDescriptor.ItemId, varType);
                }
            }
        }
    }
}
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