Редактиране

Споделяне чрез

Creating a WHERE clause for the registry provider

  • Статия

The main points to consider when creating a proper WHERE clause for the System Registry provider is that each event query must be complete and explicit. Failure to be complete and explicit will result in an error message.

To be complete, each event query in the bstrQuery parameter of ExecNotificationQueryAsync must contain a WHERE clause that includes each of the properties in the specified event class.

The following example shows how to set bstrQuery to register for tree change events in the "HKEY_LOCAL_MACHINE\Software" tree.

SELECT * FROM RegistryTreeChangeEvent  WHERE Hive = "HKEY_LOCAL_MACHINE" AND Rootpath = "Software"

To be explicit, the provider should be able to infer from the query a list of possible values for every property in the event class.

The following example shows the event query that correctly registers for tree change events.

SELECT * FROM RegistryTreeChangeEvent 
    WHERE (hive = "hkey_local_machine" AND rootpath = "software") 
    OR    (hive = "hkey_current_user" AND rootpath = "console")

The following is an example of an incorrect registration.

SELECT * FROM RegistryTreeChangeEvent  WHERE hive = "hkey_local_machine" OR rootpath ="software"

Because there is no way to evaluate the possible values for each of the properties, WMI rejects with the error WBEM_E_TOO_BROAD any query that either does not have a WHERE clause or if the WHERE clause is too broad to be of any use.