Exercise 5: Cross-Service Communication

5.1 Understanding Cross-Service Scenarios

Cross-service communication simulates real microservices architectures where:

• BookshopService handles core business operations (book promotion, inventory)
• ReviewsService manages review workflows (approval, moderation, statistics)
• Services need to synchronize data and trigger actions across domains

5.2 Implement Cross-Service Communication

1. Enhanced Books.js with cross-service functionality:

Update webapp/localService/mainService/data/Books.js to demonstrate how book operations can trigger review-related actions:

module.exports = {
  getInitialDataSet: function (contextId) {
    // ... existing code from previous exercise ...
  },

  executeAction: function (actionDefinition, actionData, keys) {
    console.log('Executing action:', actionDefinition.name);

    switch (actionDefinition.name) {
      case 'setDiscount':
        // ... existing setDiscount code ...
        break;

      case 'promoteBook':
        console.log('📚 Starting book promotion with cross-service integration...');

        // Step 1: Update book in main service
        const bookEntries = await this.base.fetchEntries(keys);
        const bookData = bookEntries[0];
        if (!bookData) {
          this.throwError('Book not found', 404);
          return;
        }

        // Update the book with promotion status
        await this.base.updateEntry(keys, {
          description: 'PROMOTED: ' + bookData.description,
          stock: bookData.stock + 10, // Add promotional inventory
        });

        console.log('✅ Book updated in BookshopService');

        // Step 2: Cross-service communication to ReviewsService
        // Add a promotional review via the reviews service
        this.base
          .getEntityInterface('Reviews', 'reviews')
          .then(function (reviewService) {
            if (reviewService) {
              console.log('🔄 Connecting to ReviewsService...');

              return reviewService.addEntry({
                ID: `promo-${Date.now()}-${Math.random().toString(36).substring(7)}`,
                book_ID: keys.ID, // Link to the promoted book
                reviewer: 'Marketing Team',
                rating: 5, // Promotional reviews are always 5-star
                comment: `📈 PROMOTIONAL: "${bookData.title}" has been featured! Don't miss this amazing read.`,
                createdAt: new Date().toISOString(),
                createdBy: 'system',
                modifiedAt: new Date().toISOString(),
                modifiedBy: 'system',
                IsActiveEntity: true,
                HasActiveEntity: false,
                HasDraftEntity: false,
              });
            }
          })
          .then(function () {
            console.log('✅ Cross-service promotional review added to ReviewsService');
          })
          .catch(function (error) {
            console.error('❌ Failed to add cross-service review:', error);
            // Don't fail the whole operation if review creation fails
          });

        return {
          message: 'Book promoted successfully with cross-service review integration!',
          promoted: true,
          crossServiceIntegration: 'Reviews service notified',
        };

      default:
        this.throwError(`Action ${actionDefinition.name} not implemented`, 501);
    }
  },
};

2. Start the application:

# from folder ex5
npm run start-mock
# or from root folder
npm run start:ex5

If you now start the app, in the List Report the data from the getInitialDataSet method of the Books.js file is shown.

If you select a book in the List Report and press the Button CAP Promote Book , the book is promoted and a promotional review is created in the ReviewsService .

As we did not integrate the Service in the List Report, we can check the created review by opening the URL http://localhost:8085/reviews/Reviews in the browser.

There should be now at least one entry with the comment:

"comment": "📈 PROMOTIONAL: \"Biography Book 1\" has been featured! Don't miss this amazing read."

5.3 Key Benefits of Cross-Service Communication

• Realistic Integration Patterns: Book promotions triggering review creation mirrors real microservices workflows
• Audit Trails: System activities are logged across service boundaries for compliance
• Service Validation: Cross-service data integrity checks ensure consistent state
• Error Resilience: Graceful handling of cross-service failures maintains system stability

Next Steps

Exercise 6 will show how to implement context-based isolation (multi-tenancy) where different tenants can have separate datasets and business logic variations using the ?sap-client= query parameter.