CTX_DBBase :: DBBeforeRead - Before read event handler

The before read event handler is called before reading an instance ( DBP_Read event).

At the time, when the handler is called, the instance is already selected in the property handle. Key data for the sort key (when defined) is available and can be copied to the instance area using the SetKey () structure context function or can be provided by using the GetKey () context function.

The handler can be used to optimize read access by returning YES or marking an instance as "hidden" ( HideInstance ()), when an instance with the given key should not be provided.

The handler can be overloaded in specialized structure context class ( CTX_Structure ) implementations.