some samples how to serve things

bookshop/srv/ord-service.cds

@@ -0,0 +1,12 @@
+// @requires: 'ORDconsumer'
+@rest @path:'/ord/v1'
+service OrdService {
+  @readonly entity documents {
+    key id: String;
+  }
+  @readonly entity csn {
+    key id: String;
+  }
+
+  function api (service: String, format: String) returns {};
+}

bookshop/srv/ord-service.mjs

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+import cds from '@sap/cds'
+export class OrdService extends cds.ApplicationService {
+  init(){
+
+    this.on('READ','documents', req => {
+      let csn = cds.context?.model || cds.model
+      return { ord: csn }
+    })
+
+    /**
+     * Just an example to do something with id, if given.
+     * Try it out with URLs like that:
+     * http://localhost:4004/ord/v1/documents
+     * http://localhost:4004/ord/v1/documents/CatalogService
+     * http://localhost:4004/ord/v1/documents/CatalogService.Books
+     * http://localhost:4004/ord/v1/documents/CatalogService.Authors
+     */
+    this.on('READ','csn', req => {
+      let csn = cds.context?.model || cds.model
+      let { id } = req.data
+      if (id) csn = csn.definitions[id] || 'not in model!'
+      return { id, csn }
+    })
+
+    /**
+     * Just an example to serve arbitrary content with a function.
+     * Try it out with URLs like that:
+     * http://localhost:4004/ord/v1/api?service=CatalogService
+     * http://localhost:4004/ord/v1/api?service=CatalogService&format=edmx
+     * http://localhost:4004/ord/v1/api?service=CatalogService&format=edmx-v2
+     * http://localhost:4004/ord/v1/api?service=CatalogService&format=openapi
+     */
+    this.on('api', req => {
+      let csn = cds.context?.model || cds.model
+      let { service, format } = req.data
+      let { res } = req.http
+      if (!format) {
+        if (!service) return res.send(csn)
+        service = csn.services[service]
+        return res.send({ definitions: [ service, ...service.entities ] .reduce ((all,e) => {
+          let d = all[e.name] = {...e}
+          delete d.projection // not part of the API
+          delete d.query     // not part of the API
+          return all
+        },{})})
+      }
+      let api = cds.compile(csn).to[format]({service})
+      return res.send(api)
+    })
+
+    return super.init()
+  }
+}