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_packages/bookshop-enhanced/db/schema.cds

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+/*
+  In this model we demonstrate how to add Genres to Books in
+  as if it was an external extension. For example we use
+  CDS Aspects' to extend the core domain model's Books entity
+  as well as the AdminService.
+ */
+
+namespace sap.capire.bookshop;
+using { sap.capire.reviews.ReviewsService as external } from '@sap/capire-reviews';
+using { sap.capire.bookshop.Books } from '@sap/capire-bookshop/db/schema';
+using { sap.common.CodeList } from '@sap/cds/common';
+
+// Extending Books by Reviews and Genres
+extend Books with {
+  reviews : Composition of many external.Reviews on reviews.subject = ID;
+  rating : external.Reviews.rating;
+  genre : Association to Genres;
+}
+
+// Hierarchical Code List for Genres
+entity Genres : CodeList {
+  key ID : Integer;
+  children : Composition of many Genres on children.parent = $self;
+  parent : Association to Genres;
+}