Adding suppliers showing integration with S/4

suppliers/srv/mashup.js

@@ -0,0 +1,52 @@
+////////////////////////////////////////////////////////////////////////////
+//
+//    Mashing up provided and required services...
+//
+module.exports = async()=>{ // called by server.js
+
+  if (!cds.services.AdminService) return //> mocking S4 service only
+
+  // Connect to services we want to mashup below...
+  const S4bupa = await cds.connect.to('API_BUSINESS_PARTNER')   //> external S4 service
+  const admin = await cds.connect.to('AdminService')            //> local domain service
+  const db = await cds.connect.to('db')                         //> our primary database
+
+  // Reflect CDS definition of the Suppliers entity
+  const { Suppliers } = S4bupa.entities
+
+  admin.prepend (()=>{
+
+    // Delegate Value Help reads for Suppliers to S4 backend
+    admin.on ('READ', 'Suppliers', async req => {
+      console.log ('>> delegating to S4 service...')
+      return await S4bupa.run(req.query)
+    })
+
+
+    // Replicate Supplier data when Books are edited
+    admin.on (['CREATE','UPDATE'], 'Books', async (req,next) => {
+      let { supplier } = req.data
+      if (supplier) {
+        let cached = await db.exists (Suppliers, supplier)
+        if (!cached) await replicate (supplier,'initial')
+      }
+      return next()
+    })
+
+  })
+
+  // Subscribe to changes in the S4 origin of Suppliers data
+  S4bupa.on ('BusinessPartner/Changed', async msg => {
+    let cached = await SELECT('ID').from (Suppliers)
+      .where ('ID in', msg.businessPartner.KEYS)
+    for (let each of cached) replicate (each)
+  })
+
+  // Helper function to replicate Suppliers data
+  async function replicate (ID,_initial) {
+    let data = await S4bupa.read (Suppliers, ID)
+    if (_initial) return db.insert (data) .into (Suppliers)
+    else return db.update (Suppliers,ID) .with (data)
+  }
+
+}