Consumption Views

The CDS projection IS the federation contract. The @federation.* annotation declares runtime behavior; the projection declares schema — what fields, what shape, what renames.

using { ProviderService as remote } from '../srv/external/ProviderService';

// 1. Wildcard — all fields, no renames (simplest case)
@federation.delegate
entity Customers as projection on remote.Customers;

// 2. Column restriction + field renames
// Remote: ID, name, category, price, currency, stock, modifiedAt (7 fields)
// Local:  productId, productName, category, unitPrice, currency (5 fields)
@federation.delegate
entity Products as projection on remote.Products {
    ID    as productId,     // rename: remote `ID` → local `productId`
    name  as productName,   // rename
    category,               // keep
    price as unitPrice,     // rename
    currency
    // remote fields `stock`, `modifiedAt` are NOT projected → never fetched
};

// 3. Field + association renames
// Enables remote→remote $expand: $expand=buyer translates to $expand=customer
@federation.delegate
entity Orders as projection on remote.Orders {
    ID         as orderId,
    customer   as buyer,      // rename association
    product    as item,       // rename association
    quantity,
    total      as amount,
    status,
    orderDate  as placedOn,
    modifiedAt
};

// 4. Entity-level rename — same remote data, different local purpose
// Remote "Customers" → local "Suppliers"
// In a procurement context, the same companies are "suppliers" not "customers"
@federation.delegate
entity Suppliers as projection on remote.Customers {
    ID    as supplierId,
    name  as companyName,
    city  as headquarters,
    country as region,
    email as contactEmail
};

From each projection, the plugin infers:

• Source service / entity from the projection on remote.X clause
• Projected columns for $select restriction (bandwidth optimization)
• Bidirectional rename mapping (localToRemote / remoteToLocal) from as clauses
• Strategy from the annotation name

A delegate query against Products translates $filter=unitPrice gt 100 to $filter=price gt 100 on the remote, then maps price → unitPrice in the response. A query against Suppliers translates $filter=companyName eq 'Acme' to $filter=name eq 'Acme' on the remote Customers entity.

!!! quote "Principle" The consumption view is the schema contract. The annotation is the runtime behavior.

Additional patterns

Excluding columns

@federation.delegate
entity CustomersLight as projection on remote.Customers excluding { email, phone };

Excluded fields are recorded in the view mapping and omitted from $select in remote calls — the plugin never fetches them, even when $select is absent on the incoming request.

Static where clauses

@federation.delegate
entity ActiveCustomers as projection on remote.Customers where blocked = false;

CAP's Consuming Services docs explicitly list where conditions as not supported on projections over remote services. This plugin extracts projection.where from the CSN at model load time and injects it into every remote query — a plugin-specific value-add.

Annotations apply only to consumption views

@federation.delegate and @federation.replicate are valid only on a CDS projection of the form entity X as projection on remote.Y. The projection is the federation contract: source service, source entity, projected columns, and bidirectional rename mapping are all inferred from it.

What this rules out:

• Annotating an imported service entity directly — annotate ReviewsService.Reviews with @federation.delegate; has no projection, so the scanner cannot infer columns or renames. Always wrap in a consumption view.
• Using plain entities as federation targets — any entity without an as projection on <remoteService>.<remoteEntity> clause is skipped.

The one escape hatch is the explicit source option on the annotation, and it is only for REST services that have no CDS model:

@federation.replicate: {
    source: 'RestProvider',
    rest: { path: '/api/customers', pagination: { type: 'offset', pageSize: 100 } }
}
entity ReplicatedRestCustomers { key ID: String(10); name: String(100); ... };

Do not use source as a general workaround for OData services — it bypasses source inference but also skips the view-mapping extraction needed for cross-service $expand, renames, and column restriction. For OData, always project on the imported service.

See also

• Terminology — how "federation", "delegation", and "replication" are used in this plugin vs. elsewhere.
• Cross-Service Scenarios — how consumption views enable cross-service $expand patterns.
• First Delegation — hands-on example.
• Annotations — complete option reference.