cleaned up

orders/srv/orders-service.js

@@ -0,0 +1,21 @@
+const cds = require('@sap/cds')
+
+module.exports = cds.service.impl(function() {
+
+  const { Books } = cds.entities
+
+  // Reduce stock of ordered books if available stock suffices
+  this.before ('CREATE', 'Orders', (req) => {
+    const { Items: OrderItems } = req.data
+    return cds.transaction(req) .run (()=> OrderItems.map (order =>
+      UPDATE (Books) .where ('ID =', order.book_ID)
+      .and ('stock >=', order.amount)
+      .set ('stock -=', order.amount)
+    )) .then (all => all.forEach ((affectedRows,i) => {
+      if (affectedRows === 0)  req.error (409,
+        `${OrderItems[i].amount} exceeds stock for book #${OrderItems[i].book_ID}`
+      )
+    }))
+  })
+
+})