perf example

performance/srv/performance-service.cds

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+using { sap.capire.performance as my } from '../db/schema';
+
+service PerformanceService {
+  entity OrdersHeaders as projection on my.OrdersHeaders;
+  entity OrdersItems   as projection on my.OrdersItems;
+  entity Books      as projection on my.Books;
+  entity Authors      as projection on my.Authors;
+
+// static
+view OrdersItemsViewJoin as select 
+
+    OrdersHeaders.ID        as Header_ID, 
+    OrdersHeaders.OrderNo   as OrderNo, 
+    OrdersHeaders.buyer     as buyer, 
+    OrdersHeaders.currency  as currency,
+    key OrdersItems.ID      as Item_ID,
+    OrdersItems.product     as product,
+    OrdersItems.quantity    as quantity,
+    OrdersItems.title       as title,
+    OrdersItems.price       as price
+
+ from OrdersHeaders JOIN OrdersItems on OrdersHeaders.ID = OrdersItems.Header.ID;
+
+// dynamic entity
+entity OrderItemsViewAssoc as projection on OrdersHeaders;
+
+// sort on right table
+view SortedOrdersJoin as select 
+    OrdersHeaders.ID        as Header_ID, 
+    OrdersHeaders.OrderNo   as OrderNo, 
+    OrdersHeaders.buyer     as buyer, 
+    OrdersHeaders.currency  as currency,
+    key OrdersItems.ID      as Item_ID,
+    OrdersItems.product     as product,
+    OrdersItems.quantity    as quantity,
+    OrdersItems.title       as title,
+    OrdersItems.price       as price
+from OrdersHeaders JOIN OrdersItems on OrdersHeaders.ID = OrdersItems.Header.ID
+order by title;
+
+// sort on items and join back to header via assoc
+
+view SortedOrdersAssoc as select
+from OrdersItems {*, Header.OrderNo, Header.buyer, Header.currency }
+order by OrdersItems.title;
+
+// filter on right table 
+
+view FilteredOrdersJoin as select 
+    OrdersHeaders.ID        as Header_ID, 
+    OrdersHeaders.OrderNo   as OrderNo, 
+    OrdersHeaders.buyer     as buyer, 
+    OrdersHeaders.currency  as currency,
+    key OrdersItems.ID          as Item_ID,
+    OrdersItems.product     as product,
+    OrdersItems.quantity    as quantity,
+    OrdersItems.title       as title,
+    OrdersItems.price       as price
+from OrdersHeaders JOIN OrdersItems on OrdersHeaders.ID = OrdersItems.Header.ID
+where price > 100;
+
+// filter on items and join back to header via assoc
+
+view FilteredOrdersAssoc as select
+from OrdersItems {*, Header.OrderNo, Header.buyer, Header.currency }
+where OrdersItems.price > 100;
+
+
+// TODO avoid CASE and/or JOIN: Denormalization of expensive complex structures, 
+// calculate on write instead of read
+
+// CASE -> try to remodel to avoid CASE, if re-modelling is not possible, 
+// fill redundant fields at write
+
+entity OrdersItemsCaseView as projection on OrdersItems {
+    *,
+    case  
+       when quantity > 500 then 'Large'
+       when quantity > 100 then 'Medium'       
+       else 'Small'
+    end as category : String
+};
+
+
+
+}
+

performance/srv/performance-service.js

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+const cds = require ('@sap/cds')
+class OrdersService extends cds.ApplicationService {
+
+  /** register custom handlers */
+  init(){
+    const { 'Orders.Items':OrderItems } = this.entities
+
+    this.before ('UPDATE', 'Orders', async function(req) {
+      const { ID, Items } = req.data
+      if (Items) for (let { product_ID, quantity } of Items) {
+        const { quantity:before } = await cds.tx(req).run (
+          SELECT.one.from (OrderItems, oi => oi.quantity) .where ({up__ID:ID, product_ID})
+        )
+        if (quantity != before) await this.orderChanged (product_ID, quantity-before)
+      }
+    })
+
+    this.before ('DELETE', 'Orders', async function(req) {
+      const { ID } = req.data
+      const Items = await cds.tx(req).run (
+        SELECT.from (OrderItems, oi => { oi.product_ID, oi.quantity }) .where ({up__ID:ID})
+      )
+      if (Items) await Promise.all (Items.map(it => this.orderChanged (it.product_ID, -it.quantity)))
+    })
+
+    return super.init()
+  }
+
+  /** order changed -> broadcast event */
+  orderChanged (product, deltaQuantity) {
+    // Emit events to inform subscribers about changes in orders
+    console.log ('> emitting:', 'OrderChanged', { product, deltaQuantity })
+    return this.emit ('OrderChanged', { product, deltaQuantity })
+  }
+
+}
+module.exports = OrdersService