add-custom-logic.md

Add Custom Logic

In this tutorial, you learn how to add custom code that changes the value of the urgency property and how CAP automatically treats the JavaScript/Java file that you add as a handler.

Prerequisites

You've implemented the user interface of your application. Follow the steps in the Add SAP Fiori Elements UIs tutorial that is part of the Develop a Full-Stack CAP Application Following SAP BTP Developer’s Guide tutorial group.

This tutorial follows the guidance provided in the SAP BTP Developer's Guide.

Add custom code

You can create a CAP project in either Node.js or Java. You have to choose one way or the other and follow through. The tabs Node.js and Java provide detailed steps for each alternative way.

[OPTION BEGIN [Node.js]]

In this tutorial, you add some custom code to the CAP application. Depending on the contents of the title property, the custom code changes the value of the urgency property.

1. In SAP Business Application Studio, go to your IncidentManagement dev space.

   Make sure the IncidentManagement dev space is in status RUNNING.

2. Create a new services.js file in the srv folder of the INCIDENT-MANAGEMENT application.

3. Add the following code (the actual business logic) to the services.js file:

   const cds = require('@sap/cds')
   
   class ProcessorService extends cds.ApplicationService {
     /** Registering custom event handlers */
     init() {
       this.before("UPDATE", "Incidents", (req) => this.onUpdate(req));
       this.before("CREATE", "Incidents", (req) => this.changeUrgencyDueToSubject(req.data));
   
       return super.init();
     }
   
     changeUrgencyDueToSubject(data) {
       let urgent = data.title?.match(/urgent/i)
       if (urgent) data.urgency_code = 'H'
     }
   
     /** Custom Validation */
     async onUpdate (req) {
       let closed = await SELECT.one(1) .from (req.subject) .where `status.code = 'C'`
       if (closed) req.reject `Can't modify a closed incident!`
     }
   }
   module.exports = { ProcessorService }

4. Make sure that the SAP Fiori application is running. If you closed it, choose the Preview Application option in the Application Info - incidents tab and select the watch-incidents npm script.

   To open the Application Info - incidents tab:

   1. Invoke the Command Palette - View → Command Palette or Command + Shift + P for macOS / Ctrl + Shift + P for Windows.
   2. Choose Fiori: Open Application Info.

5. Create a new incident with the word urgent in its title and with the urgency set to Medium.

   

   You see that the value in the Urgency field is automatically set to high.

   

[OPTION END]

[OPTION BEGIN [Java]]

In this tutorial, you add some custom code to the CAP application. Depending on the contents of the title property, the custom code changes the value of the urgency property.

1. In SAP Business Application Studio, go to your IncidentManagement dev space.

   Make sure the IncidentManagement dev space is in status RUNNING.

2. Create a new folder handler in the srv/src/main/java/customer/incident_managеment folder of your project. If srv/src/main/java/customer/incident_managеment doesn't exist, create it.

3. In the handler folder, create a new file ProcessorServiceHandler.java.

4. Add the following code (the actual business logic) to the ProcessorServiceHandler.java file:

   package customer.incident_management.handler;
   
   import cds.gen.processorservice.Incidents;
   import cds.gen.processorservice.ProcessorService_;
   import cds.gen.sap.capire.incidents.*;
   import com.sap.cds.ql.Select;
   import com.sap.cds.services.ErrorStatuses;
   import com.sap.cds.services.ServiceException;
   import com.sap.cds.services.cds.CqnService;
   import com.sap.cds.services.handler.EventHandler;
   import com.sap.cds.services.handler.annotations.Before;
   import com.sap.cds.services.handler.annotations.ServiceName;
   import com.sap.cds.services.persistence.PersistenceService;
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   import org.springframework.stereotype.Component;
   import java.util.List;
   import java.util.Locale;
   
   @Component
   @ServiceName(ProcessorService_.CDS_NAME)
   public class ProcessorServiceHandler implements EventHandler {
       private static final Logger logger = LoggerFactory.getLogger(ProcessorServiceHandler.class);
       private final PersistenceService db;
       public ProcessorServiceHandler(PersistenceService db) {
           this.db = db;
       }
       /*
       * Change the urgency of an incident to "high" if the title contains the word "urgent"
       */
       @Before(event = CqnService.EVENT_CREATE)
       public void ensureHighUrgencyForIncidentsWithUrgentInTitle(List<Incidents> incidents) {
           for (Incidents incident : incidents) {
               if (incident.getTitle().toLowerCase(Locale.ENGLISH).contains("urgent") &&
                       incident.getUrgencyCode() == null || !incident.getUrgencyCode().equals("H")) {
                   incident.setUrgencyCode("H");
                   logger.info("Adjusted Urgency for incident '{}' to 'HIGH'.", incident.getTitle());
               }
           }
       }
       /*
       * Handler to avoid updating a "closed" incident
       */
       @Before(event = CqnService.EVENT_UPDATE)
       public void ensureNoUpdateOnClosedIncidents(Incidents incident) {
           Incidents in = db.run(Select.from(Incidents_.class).where(i -> i.ID().eq(incident.getId()))).single(Incidents.class);
           if (in.getStatusCode().equals("C")) {
               throw new ServiceException(ErrorStatuses.CONFLICT, "Can't modify a closed incident");
           }
       }
   }

5. Make sure that the SAP Fiori application is running. If you closed it, navigate to the srv folder in the terminal and run mvn cds:watch.

6. Create a new incident with the word urgent in its title and with the urgency set to Medium.

   

   You see that the value in the Urgency field is automatically set to High.

   

[OPTION END]

Understand the custom code

[OPTION BEGIN [Node.js]]

Because your file is called services.js and has the same name as your application definition file services.cds, CAP automatically treats it as a handler file for the application defined in there. CAP exposes several events and you can easily write handlers like the one mentioned earlier.

[OPTION END]

[OPTION BEGIN [Java]]

Because the Java class containing the custom code is annotated with @ServiceName(ProcessorService_.CDS_NAME), CAP knows that any handler methods in the class are registered for events on entities defined in the srv/services.cds file.

The handler method itself is annotated with @Before(event = CqnService.EVENT_CREATE, entity = Incidents_.CDS_NAME). This annotation means that the method is called before each CREATE event on the entity Incidents. CAP exposes several events and you can easily write handlers like the one mentioned earlier.

[OPTION END]

In this case, the event is triggered after a READ was carried out for the Incidents entity. In your custom handler, you get all the data (in this case, all the incidents) that was read according to the query. You can loop over each of them and, if needed, adjust the data of the response. In this case, you change the value of the urgency property when the title contains the word urgent. The new values for Urgency are then part of the response to the READ request.