final state of exercise 1

packages/bookstore/srv/services.js

@@ -0,0 +1,18 @@
+const cds = require('@sap/cds')
+module.exports = async (srv) => {
+
+  const { Books } = srv.entities
+  // Check all amounts against stock before activating
+  srv.before(['CREATE', 'UPDATE'], 'Orders', (req) => {
+    const tx = cds.transaction(req), order = req.data
+    return Promise.all(order.Items.map(each => tx.run(
+      UPDATE(Books).where({ ID: each.book_ID })
+        .and(`stock >=`, each.amount)
+        .set(`stock -=`, each.amount)
+    ).then(affectedRows => {
+      if (!affectedRows) {
+        req.error(409, `${each.amount} exceeds stock for book #${each.book_ID}`)
+      }
+    })))
+  })
+}