Adding suppliers showing integration with S/4

suppliers/srv/mashup.cds

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+/*
+  Optionally add projections to external entities, to capture what
+  you actually want to use from there.
+ */
+
+using { API_BUSINESS_PARTNER as S4 } from './external/API_BUSINESS_PARTNER.csn';
+extend service S4 with {
+  entity Suppliers as projection on S4.A_BusinessPartner {
+    key BusinessPartner as ID,
+    BusinessPartnerFullName as name,
+  }
+}
+
+
+/*
+  You can mashup entities from external services, or projections
+  thereof, with your project's own entities
+ */
+using { sap.capire.bookshop.Books } from '@capire/bookshop';
+extend Books with {
+  supplier : Association to S4.Suppliers;
+}
+
+
+/*
+  You can also expose external entities through your own services
+  For this to work, you need to delegate the respective calls
+  addressed to your services into calls to the external service.
+ */
+extend service AdminService with {
+  entity Suppliers as projection on S4.Suppliers;
+}
+
+/*
+  Optionally add a local persistence to keep replicas of external
+  entities to have data in fast access locally; much like a cache.
+ */
+annotate S4.Suppliers with @cds.persistence:{table,skip:false};
+
+/**
+  Having locally cached replicas also allows us to display supplier
+  data in lists of books, which otherwise would generate unwanted
+  traffic on S4 backends.
+ */
+extend projection CatalogService.ListOfBooks with {
+  supplier
+}