The ArchiveEventPipe property of the PointList.ListData object returns an EventPipe interface that tracks archive changes to the points in the PointList. This is useful when you need to keep track of changes to history values for a collection of points, for example maintaining a consistent cache of values.
The ArchiveEventPipe tracks four kinds of updates. The EventPipe interface provides methods to view and extract the incoming events as PIEventObjects. These objects support an Action property which is used to describe the type of update the event represents. The Action property takes values from the EventActionConstants enumeration. See the settings section below for a list of Action types and their meaning.
The object placeholder is an object expression that evaluates to a ListData object, obtained from a PointList collection.
The possible values for the Action property of a PIEventObject returned from an EventPipe obtained from this property are:
|eaAdd||An event has been appended to the archive. This is the normal mode for events that pass compression tests as they move from the snapshot to the archive.|
|eaAddNoReplace||An event has been added to the archive using "No Replace" mode. This mode allows the event to be added as long as there is not already an event at the specified time. Typically out of order snapshots are sent to the archive with this mode.|
|eaDelete||An existing event has been deleted from the archive. The EventData property holds the value of the deleted event.|
|eaEdit||An existing event in the archive has been edited. The EventData property holds the new value of the event.|
The ArchiveEventPipe is not supported on PI2 servers.