In a recent assignment, I had the opportunity to use the Cloud Application Programming Model and Fiori Elements to design and create an enterprise-ready application. I used a few concepts like dynamic expressions, side effects, and custom actions on object pages. However, finding appropriate material or references with examples and understanding the concepts required a lot of time. I’ll try to briefly describe these ideas in this blog post so that others can benefit and time can be saved.

Short explanation of POC scenario and its resources

We will utilise the example project “cap-fe-se-ca-de” that I posted on GitHub here to explain the topics.  Let’s quickly review the project and some of its key files.

	Folder or File	Purpose
	app/	This has 2 ui frontends i.e. Customers and Orders
	db/	Data model is defined in schema.cds
	srv/	Services are defined in service.cds and logic is added via service.js. Also capabilities.cds adds/restricts different capabilities of the services
	app/orders	Fiori Elements based UI app for Orders annotations.cds: contains annotations for List page and Object Page annotations_se.cds: contains annotations related side effects annotations_ca_de.cds: contains annotations related to custom actions & dynamic expressions

Both the “Customers” and the “Orders” applications in the app folder were created using Fiori Elements. To better comprehend the aforementioned topics, we will concentrate on the Orders application. The first view in the Orders application is a List Page, and the second view, which is the details view, is an Object Page, as illustrated below:

Orders – List Page	Orders – Object Page

Concept-1: Side Effects

If a user modifies the content of a field or carries out an action, this modification may have an impact on other fields on the UI. This system behaviour is called a side effect.

example:  In order, if you enter quantity and price, total value gets updated automatically. This behaviour is called a side effect.

There are different variations to Side effects. Let’s explore one by one using annotations_se.cds file in Orders application.

using orderservice as service from '../../srv/service';
annotate service.Orders @(Common : {
    SideEffects #CustomerChanged : {
        SourceProperties : ['customer_ID'],
        TargetEntities   : [customer, customer.addresses]
    }
});

annotate service.OrderItems @(Common : {
    SideEffects #ProductChanged  : {
        SourceProperties : ['product_id'],
        TargetProperties : ['price', 'currency_code', 'netprice']
    }
});

annotate service.OrderItems @(Common : {
    SideEffects #QuantityChanged : {
        SourceProperties : ['quantity'],
        TargetProperties : ['netprice']
    }
});

this.before('PATCH', OrderItems, async req => {

  let productInfo, price, quantity, dbItemInfo;

  //When product is available, fill price and currency
  if (req.data.product_id != undefined && req.data.product_id != null) {
    productInfo = await cds.read(Products).byKey(req.data.product_id);
    req.data.price = productInfo.price;
    req.data.currency_code = productInfo.currency_code;
  }

  // Calculate Net Price
  dbItemInfo = await cds.read(OrderItems.drafts).where({ ID: req.data.ID });
  req.data.price > 0 ? price = req.data.price : price = dbItemInfo[0].price;
  req.data.quantity > 0 ? 
  quantity = req.data.quantity : quantity = dbItemInfo[0].quantity;
  if (price > 0 && quantity > 0) {
    req.data.netprice = price * quantity;
    req.data.netprice = Math.round((req.data.netprice + Number.EPSILON)*100);
    req.data.netprice = req.data.netprice / 100;
  }

});

annotate service.Orders @(Common : {
    SideEffects #ItemChanged     : {
        SourceEntities   : [items],
        TargetProperties : ['totamount', 'currency_code']
    }
});

this.after('PATCH', OrderItems, async data => {

  let orderInfo = { totamount: 0 };
  let result = await cds.read(OrderItems.drafts)
                        .where({ ID: data.ID }).columns(['order_ID']);
  let dbItemInfos = await cds.read(OrderItems.drafts)
                             .where({ order_ID: result[0].order_ID });
  for (let i = 0; i < dbItemInfos.length; i++) {
    if (dbItemInfos[i].netprice > 0) {
      orderInfo.totamount = orderInfo.totamount + dbItemInfos[i].netprice;
    }
    orderInfo.currency_code = dbItemInfos[i].currency_code;
  }
  await cds.update(Orders.drafts, result[0].order_ID).set(orderInfo);

});

Concept-2: DefaultValuesFunction

Default values can be supplied using a “DefaultValueFunction” when creating a new entity or item.
For example, an order’s initial status is always set to “Open” when it is created.

Annotation to provide ‘DefaultValueFunction’ is as shown below:

annotate service.Orders with @(
    Common.DefaultValuesFunction : 'getOrderDefaults'
);

Here, ‘getOrderDefaults‘ is a function of orders entity under orderservice. It is defined in service.cds  and service.js file.

//Definition [service.cds]
function getOrderDefaults() returns Orders;

//Implementation [service.js]
this.on('getOrderDefaults', async req => {
  return {status: 'Open'};
});

Concept-3: Custom Actions

The initial status of an order is ‘Open’. We can define custom action to change the status from ‘Open’ to ‘In Process’ and vice-versa.

Two bound actions and its correspoding logic are provided in service.cds and service.js respectively as shown below:

//Definition [service.cds]
entity Orders    as projection on db.Orders actions {
    action setOrderProcessing();
    action setOrderOpen(); 
};

//Implementation [service.js]
this.on('setOrderProcessing', Orders, async req => {
  await cds.update(Orders, req.params[0].ID).set({status: 'In Process'});
});

this.on('setOrderOpen', Orders, async req => {
  await cds.update(Orders, req.params[0].ID).set({status: 'Open'});
});

These 2 actions can be added in UI as Buttons using annotations as provided in annotations_ca_de.cds file.

annotate service.Orders with @(UI.Identification : [
    {
        $Type         : 'UI.DataFieldForAction',
        Label         : 'Set to In Process',
        Action        : 'orderservice.setOrderProcessing'
    },
    {
        $Type         : 'UI.DataFieldForAction',
        Label         : 'Set to Open',
        Action        : 'orderservice.setOrderOpen'
    }
]);

Concept-4: Dynamic Expressions

Dynamic expressions are small logics defined in annotation to control the behavior of UI.

Example: If status of order is Open, then only ‘Set to In Process’ button is visible and if status of order is In Process, then only ‘Set to Open’ button is visible. To achieve this, we can use dynamic expressions.

Note 1: OData supports dynamic expressions in annotations. In CDS, these dynamic expressions are provides using JSON representations. For more information, please refer this document.

annotate service.Orders with @(UI.Identification : [
    {
        $Type         : 'UI.DataFieldForAction',
        Label         : 'Set to In Process',
        Action        : 'orderservice.setOrderProcessing',
        ![@UI.Hidden] : {$edmJson : {$Ne : [{$Path : 'status'}, 'Open']}}
    },
    {
        $Type         : 'UI.DataFieldForAction',
        Label         : 'Set to Open',
        Action        : 'orderservice.setOrderOpen',
        ![@UI.Hidden] : {$edmJson : {$Eq : [{$Path : 'status'},'Open']}}
    }
]);

Criticality: {$edmJson :{$If :[{$Eq :[{$Path : 'status'},'Open']}, 1, 3]}}

Anove dynamic expression checks if status is open then return 1 else return 3 for Criticality.

Concept-5: Custom Actions with Side Effects

As explained in previous concept, We have used two action for changing the status of order. However once the action is executed, the status field on ui should also change instantly. To achieve this, we can define side effects for custom action as shown below.

In this case, side effects annotations are provided in service.cds file.

entity Orders    as projection on db.Orders actions {

    @(  cds.odata.bindingparameter.name : '_it',
        Common.SideEffects : {TargetProperties : ['_it/status']}   )
    action setOrderProcessing();

    @(  cds.odata.bindingparameter.name : '_it',
        Common.SideEffects : {TargetProperties : ['_it/status']}   )
    action setOrderOpen();
    
};

Conclusion

Together, the Cloud Application Programming Model and Fiori Elements improve developer experience while also boosting productivity and accelerating the development of enterprise-ready applications.

More information about Fiori Elements with cloud application programming model can be found here. You can follow my profile to get notification of the next blog post on CAP or Fiori Elements. Please feel free to provide any feedback you have in the comments section below and ask your questions about the topic in sap community using this link.