BTP & Integrationintermediate

BTP CAP Part 2: Building and Exposing Services with CDS

Key takeaway

Design CAP services: projections on domain entities, service-level exposure choices (read-only, restricted fields), annotations for OData and UI, mock data, hybrid testing against real BTP services with cds bind, and database deployment with cds deploy.

Explanation

📌 KEY POINTS
✅ Services expose projections of domain entities tailored to consumers (fields, read-only, filters).
✅ Annotations (@readonly, @insertonly, UI annotations) shape OData and Fiori behavior.
✅ CSV files in db/data provide mock data; cds deploy writes to the target database.
✅ cds bind connects local runs to real BTP services (e.g. HANA Cloud, XSUAA) for hybrid testing.
⚠️ Exposing domain entities one-to-one to every consumer leaks internal fields and couples UIs to the model.

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▶ WHERE WE ARE
Part 1 introduced CAP. Now services.

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▶ 1. SERVICE DESIGN

One service per consumer/use case.

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▶ 2. PROJECTIONS

Select fields, exclude, rename.

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▶ 3. ANNOTATIONS

Access, UI, OData.\n\n━━━━━━━━━━━━━━━━━━━━\n▶ 4. DATA\n• CSV mock data; cds deploy.

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▶ 5. HYBRID TESTING

cds bind; profile hybrid.

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▶ STEP BY STEP

Create AdminService and CatalogService.
Add @readonly and excluding.
Test locally, then hybrid with cds bind.

✅ CHECKPOINT: catalog users can't see cost fields.

Code example

ABAP Code

===== srv/services.cds =====using my.bookshop as my from '../db/schema';service CatalogService {  @readonly entity Books as projection on my.Books excluding { createdBy, modifiedBy, cost };}service AdminService { entity Books as projection on my.Books; } ===== HYBRID =====cds bind -2 my-hana    # binds to HANA Cloud service instancecds watch --profile hybridcds deploy --to hana   # deploy schema

Real project scenario

A Fiori app exposed the full Books entity including internal cost fields. Introducing a CatalogService projection excluding them and a separate AdminService fixed the leak.

Common mistakes

One service for all.
Exposing internal fields.
No mock data.
Testing only with SQLite.
UI logic in handlers.

Best practices

Consumer-specific services.
Projections with excluding.
CSV data.
Hybrid tests.
Use annotations.

Interview angle

Questions: "How do you design CAP services?", "What is a projection?", "What is hybrid testing?"
Strong answer: service design, projections, annotations, data, cds bind.

Practice this lesson

Quick check

1. A Fiori app exposes internal cost fields because the service exposes the full entity. What is the CAP fix?

2. Which command is used to bind a locally running CAP application to a real service instance (such as a database or destination) provisioned in Cloud Foundry, enabling hybrid testing?

3. What does the 'cds deploy' command primarily accomplish in a CAP project?

Interview questions

1. Design CAP services for a catalog app used by end users and administrators.

Answer it in your own words first, then compare.

2. How would you apply CAP in a real SAP project? Walk through the design or implementation approach.