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Lab 02 — Create a Service Projection ​

Goal ​

Expose the Location entity (from Lab 01) through the existing StarWarsPeople service, with appropriate access controls.

Prerequisite: Complete Lab 01 first.

Background ​

CDS service projections let you decide which entities to expose, under what shape, and with what constraints. This lab teaches you:

  • How to add an entity to an existing service
  • How @readonly prevents writes at the service boundary
  • How redirected to resolves associations in the service scope
  • How service-level and entity-level access annotations work together

Steps ​

Step 1 — Expose Location in the People service ​

Open srv/people-service.cds and add a Location projection inside the service StarWarsPeople block, after the last entity definition:

cds
@readonly : true
entity Location as projection on StarWars.Location {
    *, planet : redirected to Planet
};

Step 2 — Verify it appears in $metadata ​

Start the service:

bash
npm run sqlite

Then fetch the metadata and check that Location is listed:

GET http://localhost:4004/odata/v4/StarWarsPeople/$metadata

Search for Location in the XML response.

Step 3 — Test read and write behavior ​

Read (should work):

GET http://localhost:4004/odata/v4/StarWarsPeople/Location

Try to write (should be rejected with 405 Method Not Allowed):

http
POST http://localhost:4004/odata/v4/StarWarsPeople/Location
Content-Type: application/json

{ "name": "Test Location" }

Verify you get a 405 or a 400 error — @readonly blocks all mutations.

Step 4 — Add an OData test ​

Add a test to test/model.test.js (inside the existing describe block):

js
it('Location entity is exposed read-only in StarWarsPeople service', async () => {
    const { status, data } = await GET('/odata/v4/StarWarsPeople/Location')
    assert.equal(status, 200)
    assert.ok(Array.isArray(data.value), 'Should return OData value array')
})

Step 5 — Run tests ​

bash
npm run test

Expected Outcome ​

  • Location appears in $metadata for StarWarsPeople
  • GET /odata/v4/StarWarsPeople/Location returns HTTP 200
  • POST to Location is rejected (read-only)
  • New test passes

Hints ​

  • @readonly is a shorthand for @Capabilities.Insertable: false, @Capabilities.Updatable: false, @Capabilities.Deletable: false.
  • redirected to Planet is needed so that OData $expand=planet works — without it, the association target is unresolved in the service scope.
  • If you get a compile error about Location not being found, make sure you added it inside the namespace star.wars; block in schema.cds.

Stretch Exercise ​

Make Location writable (remove @readonly) and add it to services-auth.cds so that only Editor role users can create or update Locations.