Building Modern Applications with SAP CAP

Building Modern Applications with SAP CAP

A comprehensive guide to developing enterprise applications using the SAP Cloud Application Programming Model

The SAP Cloud Application Programming Model (CAP) is a framework of languages, libraries, and tools for building enterprise-grade services and applications. It guides developers through proven best practices and accelerates development with pre-built solutions for common tasks.

Why Choose SAP CAP?

CAP provides a declarative approach to building business applications, allowing developers to focus on domain logic rather than technical complexities. Key benefits include:

  • Reduced Boilerplate: Focus on business logic, not infrastructure code
  • Best Practices Built-in: Security, multitenancy, and extensibility out of the box
  • Technology Agnostic: Support for Node.js and Java runtimes
  • Cloud Native: Designed for cloud deployment from the ground up

Core Concepts

Domain Modeling with CDS

Core Data Services (CDS) is the backbone of CAP, providing a powerful way to define your domain model:

entity Products {
  key ID : Integer;
  name : String(100);
  description : String;
  price : Decimal(10,2);
  stock : Integer;
  category : Association to Categories;
}

entity Categories {
  key ID : Integer;
  name : String(50);
  products : Association to many Products on products.category = $self;
}

Service Definition

Services expose your domain model through RESTful APIs and OData:

service CatalogService {
  entity Products as projection on db.Products;
  entity Categories as projection on db.Categories;
  
  action replenishStock(product: Products:ID, quantity: Integer);
}

Building Your First CAP Application

Step 1: Project Setup

Initialize a new CAP project:

cds init my-bookshop
cd my-bookshop
npm install

Step 2: Define Your Domain Model

Create your data model in db/schema.cds:

namespace my.bookshop;

entity Books {
  key ID : Integer;
  title  : String;
  author : Association to Authors;
  stock  : Integer;
}

entity Authors {
  key ID : Integer;
  name   : String;
  books  : Association to many Books on books.author = $self;
}

Step 3: Create Services

Define services in srv/catalog-service.cds:

using my.bookshop as my from '../db/schema';

service CatalogService {
  @readonly entity Books as projection on my.Books;
  @readonly entity Authors as projection on my.Authors;
}

Step 4: Add Business Logic

Implement custom logic in srv/catalog-service.js:

module.exports = (srv) => {
  srv.after('READ', 'Books', (books) => {
    books.forEach(book => {
      if (book.stock > 100) book.title += ' -- Bestseller!'
    })
  })
}

Advanced Features

Authentication and Authorization

CAP provides built-in support for authentication:

service CatalogService @(requires: 'authenticated-user') {
  entity Books @(restrict: [
    { grant: 'READ', to: 'Viewer' },
    { grant: '*', to: 'Admin' }
  ]) as projection on my.Books;
}

Multitenancy

Enable SaaS applications with built-in multitenancy support:

{
  "cds": {
    "requires": {
      "multitenancy": true,
      "extensibility": true
    }
  }
}

Draft Handling

Support for draft-enabled entities:

service CatalogService {
  @odata.draft.enabled
  entity Books as projection on my.Books;
}

Deployment Options

SAP BTP Cloud Foundry

Deploy to Cloud Foundry with a simple push:

cf push

Kyma Runtime

Deploy as microservices on Kubernetes:

cds build --production
pack build myapp --builder paketobuildpacks/builder:base

Best Practices

  1. Use CDS for Everything: Leverage CDS for data models, service definitions, and UI annotations
  2. Follow Domain-Driven Design: Structure your application around business domains
  3. Implement Proper Error Handling: Use CAP’s error classes for consistent error responses
  4. Write Tests Early: Use CAP’s testing utilities for unit and integration tests
  5. Monitor Performance: Implement logging and monitoring from the start

Integration with SAP Services

CAP applications integrate seamlessly with SAP services:

  • SAP HANA: Native support for HANA-specific features
  • SAP Event Mesh: Built-in messaging capabilities
  • SAP Workflow: Process automation integration
  • SAP Document Management: File handling services

Conclusion

SAP CAP dramatically simplifies enterprise application development while ensuring best practices and enterprise-grade capabilities. Its declarative approach, combined with powerful abstractions, enables developers to build sophisticated applications with minimal effort.

In our next post, we’ll explore how to implement event-driven architectures using SAP Event Mesh and CAP.

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