Getting object instances through querying and filtering

  • Article

This topic provides an overview of how to retrieve the instances of a class from a CIM server.

In this scenario, a cmdlet retrieves zero, one, or many instances of a class. There are several ways to retrieve class instances from a CIM server.

  • GetInstance
  • QueryInstances
  • EnumerateInstances
  • EnumerateAssociatedInstances

Currently CDXML does not support GetInstance for retrieving a particular instance. Server filtering can be done through QueryInstances; however, CDXML supports WQL queries only.

A GET cmdlet definition based on Enumerate and Query requires the following information.

  • Metadata that describes the cmdlet properties.

    • Verb
    • Noun
    • HelpURI

  • Cmdlet parameters for filtering the results.

    • Cmdlet parameter Name and Type
    • Cmdlet parameter attributes (Mandatory, ValueFromPipeline, Position, and so on)
    • CIM class property used for filtering
    • Type of filter query expressions to be formed. For example, RegularQuery or MinQuery

  • For each parameter, the form of its query expression can be further specialized into one of the following types:

    • RegularQuery - Compares an instance property value with the corresponding cmdlet argument using either the equal or like operator.
    • MinQuery - Compares an instance property value with the corresponding cmdlet argument value using the less than or equal operator.
    • MaxQuery - Compares an instance property value with the corresponding cmdlet argument value using the greater than or equal operator.
    • ExcludeQuery - Compares an instance property value with the corresponding cmdlet argument value and filters out instances that match.

The information above applies to the GET cmdlet when working with instance providers; that is, a CIM provider that returns instances through QueryInstance or EnumerateInstances intrinsic operations.

The following CDXML elements are used to describe the information outlined above.

Cmdlet Metadata : <Cmdlet> and <CmdletMetadata> 
Cmdlet Filterting Parameters : <GetCmdletParameters>