Documented impl

bookshop/srv/cat-service.js

@@ -1,25 +1,30 @@
 const cds = require('@sap/cds')
-const { Books } = cds.entities ('sap.capire.bookshop')
 
 class CatalogService extends cds.ApplicationService { init(){
 
+  // Reflect entities from model
+  const { Books } = cds.entities ('sap.capire.bookshop')
+
   // Reduce stock of ordered books if available stock suffices
   this.on ('submitOrder', async req => {
     const {book,amount} = req.data
-    let {stock} = await SELECT('stock').from(Books,book)
+    // Read stock from database
+    let {stock} = await SELECT.from (Books, book, b => b.stock)
     if (stock >= amount) {
-      await UPDATE (Books,book).with ({ stock: stock -= amount })
+      // Reduce stock by ordered amount
+      await UPDATE (Books,book) .with ({ stock: stock -= amount })
+      // Emit event to inform others
       await this.emit ('OrderedBook', { book, amount, buyer:req.user.id })
-      return { stock }
+      // Return reduced stock to caller
+      return req.reply ({ stock })
     }
+    // Return error about insufficient stock
     else return req.error (409,`${amount} exceeds stock for book #${book}`)
   })
 
   // Add some discount for overstocked books
   this.after ('READ','Books', each => {
-    if (each.stock > 111) {
-      each.title += ` -- 11% discount!`
-    }
+    if (each.stock > 111) each.title += ` -- 11% discount!`
   })
 
   return super.init()