#26 RAP or abap2UI5 — When to Use Which
The honest answer is that most systems end up with both, and the question is never "which framework" but "which one for this screen".
| RAP with Fiori Elements | abap2UI5 | |
|---|---|---|
| Backend | CDS views, behavior definitions, OData V4 | ABAP classes producing an XML view and a JSON model |
| Frontend | a Fiori Elements app per service | one static UI5 shell, shared by every app |
| UI definition | UI annotations on CDS | XML views written in ABAP |
| Data model | fixed at design time in CDS | design time, or at runtime from internal tables |
| Drafts | RAP drafts, on the model | serialization, on the app |
| Communication | OData V4 — metadata, entities, actions | HTTP, two strings per request |
| Deployment | frontend and backend transported separately | activating the class |
Here is the split that holds up in practice.
Reach for RAP when the behaviour matters more than the screen. A transactional object with validations, determinations, authorizations and draft handling — and more than one consumer for it. The moment a second client exists, or is likely to, the behaviour needs to live somewhere that is not a UI, and RAP is where SAP put it. Standard CRUD over a stable model, close to what a list report or an object page already does, is the case it was built for and the case where it costs the least.
Reach for abap2UI5 when the screen is the deliverable. One consumer, one purpose, and often a short life: an operations tool, a correction screen, a form somebody needs by Thursday, a dashboard for one team. Also whenever the shape is not known until runtime — a table whose columns come from RTTI — or when the screen needs a control the annotation vocabulary does not reach. And on an older release, where RAP is not available at all.
The two are not exclusive, and this is the part worth remembering. An abap2UI5 app calls a RAP business object through EML like any other consumer. The validations still run, the draft still works, the authorizations still apply. So a screen that RAP cannot shape the way it needs to be shaped is not a reason to abandon the business object — only a reason to put a different UI in front of it.
Rule of thumb: model the behaviour once, in RAP, if more than one thing will use it. Build the screen wherever it is cheapest.
Happy ABAPing! 🦖🦕🦣