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Retrieving a WMI Instance

  • Artikkeli

Retrieving an instance is one of the most common retrieval procedures you are likely to perform in WMI. You can retrieve an existing instance or create a new unnamed instance. The WMI path to the existing instance is a required parameter. For more information, see Describing the Location of a WMI Object.

Note

When providing an instance, a provider may be unable to provide a value for certain properties. Unless otherwise stated in the property description, you cannot infer any meaning from an empty value. This is not to be confused with a string which has a NULL value. In this case, the value is populated. It is empty but has a value: NULL.

 

Retrieve a local copy of the instance with a call to the PowerShell Get-WmiObject cmdlet.

To retrieve an instance of a WMI class using PowerShell

  • You can retrieve specific instances using the -class and -filter parameters.

    Get-WmiObject -query "SELECT * FROM Win32_logicalDisk WHERE DeviceID = 'C:'"

You can retrieve a WMI instance using C# by creating a search object using CimInstance, and then filling it with the relevant key values, and then searching for that object with a CimSession.GetInstance call.

To retrieve an instance of a WMI class using C# (Microsoft.Management.Infrastructure)

  1. Using the Microsoft.Management.Infrastructure namespace, create a new CimInstance object with the relevant class name and namespace.

    using Microsoft.Management.Infrastructure;
...
string Namespace = @"root\cimv2";
string className = "Win32_LogicalDisk";

CimInstance myDrive = new CimInstance(className, Namespace);

  2. Create a CimProperty that contains the name and value of the key property of the instance you wish to search for, and add that property to your class object.

    myDrive.CimInstanceProperties.Add(CimProperty.Create("DeviceID", "C:", CimFlags.Key));

  3. Retrieve the object from WMI with a CimSession.GetInstance call.

    CimSession mySession = CimSession.Create("localhost");
CimInstance searchInstance = mySession.GetInstance(Namespace, myDrive);

You can retrieve either a specific WMI class instance, or a collection of WMI class instances, using classes in the System.Management namespace.

Note

System.Management was the original .NET namespace used to access WMI; however, the APIs in this namespace generally are slower and do not scale as well relative to their more modern Microsoft.Management.Infrastructure counterparts.

 

To retrieve an instance of a WMI class using C# (System.Management)

  1. Retrieve a local copy of a specific instance by creating a new ManagementObject, with the name and specific instance value passed in though the ManagementPath parameter. You can then retrieve the instance data by explicitly calling ManagementObject.Get.

    using System.Management;
...
ManagementObject objInst = new ManagementObject("Win32_LogicalDisk.DeviceID='C:'");
objInst.Get();

  2. Alternately, you can retrieve all instances of a WMI class by searching for them with a ManagementObjectSearcher, and then enumerating through the returned ManagementObjectCollection.

    using System.Management;
...
ManagementObjectSearcher mgmtObjSearcher = new ManagementObjectSearcher("SELECT * FROM Win32_LogicalDisk");
ManagementObjectCollection colDisks = mgmtObjSearcher.Get();

foreach (ManagementObject objDisk in colDisks)
{
   Console.WriteLine("Device ID : {0}", objDisk["DeviceID"]);
}

Console.ReadLine();

    You can implicitly call the Get method by accessing the instance. For more information, see Retrieving Part of a WMI Instance.

Retrieve a local copy of the instance with a call to the VBScript GetObject method.

To retrieve an instance of a WMI class using VBScript

  • Call GetObject with the object path of the instance as shown in the following example.

    Set objinst = GetObject("WinMgmts:Win32_LogicalDisk='C:'")

    Retrieving a specific instance requires giving a name as part of the object path.

In C++, call IWbemServices::GetObject.

To retrieve an instance of a WMI class using C++