delegate-consumption-view

name	delegate-consumption-view
description	Creates @federation.delegate consumption views on remote OData entities in SAP CAP. Use when proxying remote data, adding field renames, association renames, read-only defaults, CUD opt-in, or delegate caching.

Delegate consumption view

Minimal pattern

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

@federation.delegate
entity Customers as projection on remote.Customers;

Common patterns

Column restriction + renames — excluded fields are never fetched remotely:

@federation.delegate
entity Products as projection on remote.Products {
    ID    as productId,
    name  as productName,
    price as unitPrice,
    currency
};

Association renames — $expand=buyer maps to remote $expand=customer:

@federation.delegate
entity Orders as projection on remote.Orders {
    ID       as orderId,
    customer as buyer,
    product  as item
};

Static filter — injected into every remote query:

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

CUD opt-in (read-only by default)

// All CUD:
@federation.delegate: { writable: true }
entity Products as projection on remote.Products { * };

// Selective:
@federation.delegate: { create: true, update: true }
entity Partners as projection on remote.Partners { ... };

Disabled operations return HTTP 405.

Optional cache

@federation.delegate: { cache: { ttl: 60000 } }
entity CachedCustomers as projection on remote.Customers;

Default strategy is response (requires cds-caching). Use strategy: 'entity' for full-entity SQLite snapshots (requires cds-data-pipeline).

Anti-patterns

❌ Wrong — entity without projection on remote.X:

@federation.delegate
entity Products { key ID: UUID; name: String; }

✅ Correct — always use a consumption view projection.

❌ Wrong — assuming CREATE/UPDATE/DELETE work without write flags.

✅ Correct — explicit writable: true or per-operation flags.

❌ Wrong — hand-written srv.on('READ', ...) for the same entity.

✅ Correct — let the plugin register the delegate handler from the annotation.

Docs

• Annotations: https://mikezaschka.github.io/cds-data/federation/reference/annotations.html
• Consumption views: https://mikezaschka.github.io/cds-data/federation/concepts/consumption-views.html