rebuild sample to self cont

multitenancy/srv/cat-service.js

@@ -0,0 +1,26 @@
+const cds = require('@sap/cds')
+const { Books } = cds.entities ('sap.capire.bookshop')
+
+class CatalogService extends cds.ApplicationService { init(){
+
+  // 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)
+    if (stock >= amount) {
+      await UPDATE (Books,book) .with (`stock -=`, amount)
+      await this.emit ('OrderedBook', { book, amount, buyer:req.user.id })
+      return { stock }
+    }
+    else return req.error (409,`${amount} exceeds stock for book #${book}`)
+  })
+
+  // Add some discount for overstocked books
+  this.after ('READ','ListOfBooks', each => {
+    if (each.stock > 111) each.title += ` -- 11% discount!`
+  })
+
+  return super.init()
+}}
+
+module.exports = { CatalogService }