How to: Query for Specific Instances of a Class (C#)

  • Article

This topic provides step-by-step instructions for querying instances of a class with WQL (WMI Query Language) using the Windows Management Infrastructure (MI) .NET API. In addition to the steps, a full source code example is provided at the end of the topic.

Note

To see the native MI API and Microsoft Visual C++ version of this topic, refer to How to: Query for Specific Instances of a Class (C/C++)

 

Step-by-step Instructions

  1. Add a reference to the Microsoft.Management.Infrastructure reference assembly. (This assembly ships as part of the Windows Software Development Kit (SDK) for Windows 8.)

  2. Add a using statement for the Microsoft.Management.Infrastructure namespace.

    using Microsoft.Management.Infrastructure;

  3. Instantiate a CimSession object. The following snippet uses the standard "localhost" value for the CimSession.Create method.

    CimSession cimSession = CimSession.Create("localhost");

  4. Call the CimSession.QueryInstances method passing the desired CIM namespace and WQL to use. The following snippet will return two instances representing two standard Windows processes where the handle property (representing a process ID, or PID) has a value of either 0 or 4.

    IEnumerable<CimInstance> queryInstances =     
  cimSession.QueryInstances(@"root\cimv2", 
                            "WQL", 
                            @"select name from win32_process where handle = 0 or handle = 4");

  5. Loop through the returned CimInstance objects.

    foreach (CimInstance cimInstance in enumeratedInstances)
{ 
  Console.WriteLine("Process name: {0}", cimInstance.CimInstanceProperties["Name"].Value);  
}

Example

The following code sample enumerates all instances of the Win32_Process class (which represents active processes) on the local machine, and prints the name of each process.

Note

In a real application you would define as parameters the computer name ("localhost") and CIM namespace ("root\cimv2"). For purposes of simplicity, these have been hardcoded in this example.

 

using System;
using System.Collections.Generic;
using Microsoft.Management.Infrastructure;

public partial class MI
{
    static void PrintCimInstance(CimInstance cimInstance)
    {
        Console.ForegroundColor = ConsoleColor.Blue;
        Console.WriteLine("{0} properties", cimInstance.CimSystemProperties.ClassName);
        Console.ResetColor();

        Console.WriteLine(String.Format("{0,-5}{1,-30}{2,-15}{3,-10}", 
                                        "Key?", "Property", "Type", "Value"));

        foreach (var enumeratedProperty in cimInstance.CimInstanceProperties)
        {
            bool isKey = ((enumeratedProperty.Flags & CimFlags.Key) == CimFlags.Key);

            if (enumeratedProperty.Value != null)
            {
                Console.WriteLine(
                    "{0,-5}{1,-30}{2,-15}{3,-10}",
                    isKey == true ? "Y" : string.Empty,
                    enumeratedProperty.Name,
                    enumeratedProperty.CimType,
                    enumeratedProperty.Value);
            }
        }
        Console.WriteLine();
    }

    public static void QueryInstance(string query)
    {
        try
        {
            CimSession cimSession = CimSession.Create("localhost");

            IEnumerable<CimInstance> queryInstances = 
              cimSession.QueryInstances(@"root\cimv2", "WQL", query);
            foreach (CimInstance cimInstance in queryInstances)
            {
                //Use the current instance. This example prints the instance. 
                PrintCimInstance(cimInstance);
            }
        }
         catch (CimException ex) 
        { 
            // Handle the exception as appropriate.
            // This example prints the message.
            Console.WriteLine(ex.Message); 
        }
    }
}

C# 
using System;

namespace MIClientManaged
{
class Program
{
static void Main(string[] args)
{
while (true)
{
Console.Write("Enter WQL (x = Quit): ");
string query = Console.ReadLine().ToUpper();
if (query.CompareTo("X") == 0) break;
MI.QueryInstance(query);
}
}
}
}