RAP Query Provider Class Implementation (if_rap_query_provider)

A custom entity in ABAP RESTful Application Programming Model (RAP) is a special entity type that a developer uses to expose data that does not originate from a standard CDS view or database table — for example, data retrieved from a remote on-premise system via RFC. The developer implements an associated query implementation class to define how data is fetched and returned, including support for filtering, as described in tutorials such as RFC: Get Data from an On-Premise System Using a Custom Entity and RFC: Enhance the Handler Class With Filtering. A remote client proxy can then be used alongside the custom entity to call the remote system and surface the results through an OData service.