IEventSystem::Query method (eventsys.h)
Retrieves a collection of subscription or event objects from the event data store.
HRESULT Query(
[in] BSTR progID,
[in] BSTR queryCriteria,
[out] int *errorIndex,
[out, retval] IUnknown **ppInterface
);
[in] progID
The ProgID of the object class to be queried. This must be a valid event object class identifier. This parameter can be one of the following values:
- PROGID_EventClass
- PROGID_EventClassCollection
- PROGID_EventSubscription
- PROGID_EventSubscriptionCollection
[in] queryCriteria
The query criteria. For details on forming a valid expression for this parameter, see the Remarks section below.
[out] errorIndex
The location, expressed as an offset, of an error in the queryCriteria parameter.
[out, retval] ppInterface
Address of a pointer to the object obtained as a result of the query. This parameter cannot be NULL. Depending on the object specified by the progID parameter, this is a pointer to one of the following interfaces:
This method can return the standard return values E_INVALIDARG, E_POINTER, E_OUTOFMEMORY, E_UNEXPECTED, and E_FAIL, as well as the following values.
Return code | Description |
---|---|
|
The method completed successfully. |
|
A syntax error occurred while trying to evaluate a query string. |
|
An invalid field name was used in a query string. |
The caller is responsible for freeing memory allocated through the ppInterface parameter.
The query criteria specified by the queryCriteria parameter can be "ALL", to specify a request for all subscription objects, or a Boolean expression denoting one or more conditions a subscription object must meet to be included in the query result. Valid expressions are of the following form:
[NOT] propertynamerelationalOperatorvalue. Valid relational operators are as follows:
==, =, !=, <>, ~=. Valid values are "string", 'string', {GUID}, TRUE, FALSE, NULL.
Individual Boolean expressions can be joined with AND or OR. Expressions can be nested in parentheses to enforce a specific order of evaluation.
Following are some examples of valid query criteria:
"EventClassID == {F89859D1-6565-11D1-88C8-0080C7D771BF}"
"EventClassID == {F89859D1-6565-11D1-88C8-0080C7D771BF} AND MethodName = 'StockPriceChange'"
Requirement | Value |
---|---|
Minimum supported client | Windows 2000 Professional [desktop apps only] |
Minimum supported server | Windows 2000 Server [desktop apps only] |
Target Platform | Windows |
Header | eventsys.h |