Registering a Class Provider
To create a WMI class provider you must register the __Win32Provider instance that represents your provider using an instance of __ClassProviderRegistration. As a COM object, your provider must register with the operating system and WMI. The following procedure assumes that you have already implemented the registration process as described in Registering a Provider. If your provider stores most data in the WMI repository and that data is updated only on WMI initialization, then register your class as a push class provider. If the data you are providing changes frequently and is retrieved dynamically by your code on every request from WMI, then register your provider as a pull class provider.
The following procedure describes how to register a push class provider.
To register a push class provider
- Set the InteractionType property of the
__ClassProviderRegistration instance to 1.
Creating an instance of __ClassProviderRegistration is part of the registration process.
The following procedure describes how to register a pull class provider.
To register a pull class provider
- Create an instance of the __Win32Provider class that describes the provider.
- Create an instance of the
__ClassProviderRegistration class that describes the feature set of the provider.
Within the __ClassProviderRegistration instance:
- Set the InteractionType property to indicate whether the provider is a push or pull provider.
- Tag the class with both the Dynamic and Provider qualifiers.
- Define the ResultSetQueries, ReferencedSetQueries, and UnsupportedQueries properties.
These query properties describe detailed information about the supported class.
In addition to describing the various supported methods of a class, the __ClassProviderRegistration class also has three properties that describe a series of queries. When used together, these three properties describe the entire range of classes supplied by the class provider. Each query property contains a WQL SELECT statement, called a "schema query," to specify the types of supported classes. Schema queries specify a special class name called meta_class. The following table lists the query properties.
|ResultSetQueries||Contains information about the result set the provider supplies. WMI uses the information to determine whether to invoke the provider to satisfy a query from an application. This property describes either the set of all classes that the provider can supply or a superset of the available classes, but never a subset. WMI requires a provider to specify at least one query in this property.
The following example shows how to set ResultSetQueries when a provider supplies an association class that references the Win32_LogicalDisk class.
The following example shows how to specify a general query when a provider supplies classes that reference other unknown classes.
The following example shows how to set ResultSetQueries when a provider supplies only subclasses, but not the parent class of a given class.
The following example shows how to use the special __this property and set ResultSetQueries when a provider supplies all class and subclasses.
|ReferencedSetQueries||Determines whether to bypass the provider in schema queries where associations and references are being requested. Providers that can supply association classes must include at least one query in their ReferencedSetQueries property.|
|UnsupportedQueries||Contains information about the result set that a class provider does not supply. WMI uses this property to subtract from the set of classes implied by ResultSetQueries. For example, a class provider can specify in ResultSetQueries support for all classes derived from MyClass and specify in UnsupportedQueries a lack of support for one particular derived class.
The more information that a provider can register about its query processing capabilities, the faster it runs. Entering one or more queries in the UnsupportedQueries property is one way to be specific and is particularly important when a provider relies on a class that it does not supply. When a request is made for a class that is listed in a query in the UnsupportedQueries property, WMI can supply the class itself or invoke an alternate provider to supply it.
Because WMI does not support the OR clause, you must create a separate query for each class.
The following queries are specified in ResultSetQueries when a class provider supplies MyClass1, MyClass2, and MyClass3.
SELECT * FROM meta_class WHERE __Class = "MyClass1" SELECT * FROM meta_class WHERE __Class = "MyClass2" SELECT * FROM meta_class WHERE __Class = "MyClass3"