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references/design-patterns.md
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references/design-patterns.md
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# SAP BTP Design Patterns Reference
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## Overview
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Design patterns provide guidance for creating superior user experiences, implementing secure architectures, and building well-modularized applications on SAP BTP.
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## User Experience Design
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### Core Principle
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Superior UX drives business value through:
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- Improved productivity
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- Better data quality
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- Higher user adoption
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### Common Challenges
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| Challenge | Impact |
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|-----------|--------|
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| Information discovery | Users can't find data |
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| Data fragmentation | Multiple systems to check |
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| Excessive navigation | Wasted time |
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| Poor error handling | User frustration |
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### Design Thinking
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**Approach**: Understand user needs through observation and feedback
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**Process:**
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1. Empathize - Understand users
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2. Define - Clarify problems
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3. Ideate - Generate solutions
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4. Prototype - Build quickly
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5. Test - Validate with users
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**Motto**: "Fail fast, fail early"
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## Development Use Case Patterns
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### Process Automation
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**Type**: Low-code/no-code
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**Tool**: SAP Build Process Automation
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**Best For**: Business experts creating workflows
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### Web and Mobile Applications
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**Tool**: SAP Build Apps, MDK
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**Best For**: Cross-platform consumer applications
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### Full-Stack Development
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**Types:**
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- Single-tenant applications
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- Multitenant SaaS applications
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- Tenant-specific extensions
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**Reference Apps:**
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- Poetry Slam Manager (SaaS)
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- Catering Management (Extension)
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- Incident Management (Full-stack)
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## Technology Design
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### Modularization Benefits
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| Benefit | Description |
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|---------|-------------|
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| Maintainability | Easier to understand and modify |
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| Testability | Independent unit testing |
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| Scalability | Scale individual components |
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| Reduced coupling | Changes don't cascade |
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| Faster innovation | Independent development |
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### Domain-Driven Design (DDD)
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**When to Use**: Applications with 30+ use cases, complex domains
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**Recommended Approach (SAP BTP/CAP):**
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1. **SAP One Domain Model**: Leverage SAP's standardized business data model for consistency across SAP solutions
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2. **CAP Domain Modeling**: Use CDS for human-readable, business-aligned domain models
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3. **Community Practices**: Apply EventStorming, bounded-context discovery for complex scenarios
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**Complexity Scoring Heuristic**:
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> **Note**: This scoring is a pragmatic heuristic to help decide when deeper DDD practices (EventStorming, bounded-context discovery) may provide value. Always validate triggers against domain expert input, non-functional requirements (performance, scalability), and team constraints before applying.
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| Criterion | Points | Consideration |
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|-----------|--------|---------------|
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| 30+ use cases | 2 | Scale indicator |
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| Anticipated growth | 1 | Future complexity |
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| Significant future changes | 2 | Maintainability needs |
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| Novel domain | 2 | Unknown complexity |
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**Score 7+ points**: Consider deeper DDD practices
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**DDD Process** (8 steps from ddd-crew):
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1. Align business goals
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2. Discover domain
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3. Decompose domain
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4. Connect bounded contexts
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5. Strategize models
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6. Define domain events
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7. Design bounded contexts
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8. Evolve architecture
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**Resources:**
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- SAP One Domain Model: [https://api.sap.com/sap-one-domain-model](https://api.sap.com/sap-one-domain-model)
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- CAP Domain Modeling: [https://cap.cloud.sap/docs/guides/domain-modeling](https://cap.cloud.sap/docs/guides/domain-modeling)
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- DDD Starter Modeling: [https://github.com/ddd-crew/ddd-starter-modelling-process](https://github.com/ddd-crew/ddd-starter-modelling-process)
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## CAP Design Principles
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### Domain-Driven Development
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- Collaborate with domain experts
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- Use CDS for human-readable models
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- Focus on business concepts
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### Out-of-the-Box Best Practices
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CAP provides automatic:
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- OData service generation
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- CRUD operations
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- Authorization checks
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- Audit logging
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### Platform Agnostic Design
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CAP abstracts:
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- Deployment targets (CF, Kyma)
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- Authentication methods
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- Protocols (REST, OData, GraphQL)
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- Database technologies
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- Messaging systems
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## ABAP Design Principles
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### Model-Driven Architecture
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**Benefits:**
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- Common architecture reduces boilerplate
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- Patterns transfer across implementations
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- Built-in mock frameworks
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- Consistent code quality
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### Use Case Patterns
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**Customer Applications:**
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- Decoupled lifecycles
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- Independent workload management
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- Hub scenarios
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**Partner Solutions:**
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- Multitenant SaaS
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- Add-on products
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**Other:**
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- Mobile applications
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- Business automation
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- Code quality analysis
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## Security Design
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### Five Guidelines
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| Guideline | Focus |
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|-----------|-------|
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| Secure User Interfaces | SAP Fiori authentication, validation |
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| Access Control Models | RBAC/ABAC with OAuth/OpenID Connect |
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| API Security | OAuth 2.0, TLS encryption |
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| Secure Extensibility | Isolate and validate custom logic |
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| Domain Model Validation | Review CDS models for data protection |
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### Secure SDLC
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**Explore Phase:**
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- Implement OWASP standards
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- Train development teams
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- Conduct risk assessments
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- Plan compliance requirements
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**Discover Phase:**
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- Map data flows
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- Establish secure architecture
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- Validate third-party services
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- Incorporate security in prototypes
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**Design Phase:**
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- Apply least privilege
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- Implement defense in depth
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- Validate inputs at boundaries
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## Microservices Patterns
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### When to Use
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**Benefits:**
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- Independent scaling
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- Technology flexibility
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- Team autonomy
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**Considerations:**
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- Increased complexity
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- Network latency
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- Distributed transactions
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### CAP Approach
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Start monolithic, extract services when:
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- Different scaling needs
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- Different team ownership
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- Independent deployment required
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### Communication Patterns
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| Pattern | Use Case |
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|---------|----------|
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| Synchronous (REST/OData) | Real-time queries |
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| Asynchronous (Events) | Decoupled processes |
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| Event Sourcing | Audit requirements |
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## Database Design
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### CAP with CDS
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```cds
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// Domain model
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entity Orders {
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key ID : UUID;
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customer : Association to Customers;
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items : Composition of many OrderItems on items.order = $self;
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status : Status;
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}
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entity OrderItems {
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key ID : UUID;
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order : Association to Orders;
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product : Association to Products;
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quantity : Integer;
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}
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```
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### ABAP with CDS
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```abap
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define root view entity ZI_Order
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as select from zorder
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composition [0..*] of ZI_OrderItem as _Items
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{
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key order_uuid as OrderUUID,
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customer_id as CustomerID,
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_Items
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}
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```
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## API Design
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### API-First Approach
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1. Design API before implementation
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2. Use OpenAPI/OData specifications
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3. Follow SAP API Style Guide
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4. Publish to API Business Hub
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### Versioning Strategy
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```
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/api/v1/orders # Version 1
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/api/v2/orders # Version 2 (breaking changes)
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```
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## Testing Patterns
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### Test Pyramid
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```
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/\
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/ \ E2E Tests (few)
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/----\
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/ \ Integration Tests (some)
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/--------\
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/ \ Unit Tests (many)
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/------------\
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```
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### CAP Testing
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```javascript
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const cds = require('@sap/cds');
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describe('OrderService', () => {
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let srv;
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beforeAll(async () => {
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srv = await cds.connect.to('OrderService');
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});
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it('creates order', async () => {
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const order = await srv.create('Orders', {
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customerID: '123'
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});
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expect(order.ID).toBeDefined();
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});
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});
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```
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### ABAP Testing
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```abap
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CLASS ltcl_order DEFINITION FOR TESTING.
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METHODS test_create_order FOR TESTING.
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ENDCLASS.
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CLASS ltcl_order IMPLEMENTATION.
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METHOD test_create_order.
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" Test implementation
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cl_abap_unit_assert=>assert_not_initial( lv_order_id ).
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ENDMETHOD.
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ENDCLASS.
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```
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## Source Documentation
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- Design (CAP): [https://github.com/SAP-docs/btp-developer-guide/blob/main/docs/design-6bb7339.md](https://github.com/SAP-docs/btp-developer-guide/blob/main/docs/design-6bb7339.md)
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- Design (ABAP): [https://github.com/SAP-docs/btp-developer-guide/blob/main/docs/design-314ae3e.md](https://github.com/SAP-docs/btp-developer-guide/blob/main/docs/design-314ae3e.md)
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- Technology Design: [https://github.com/SAP-docs/btp-developer-guide/blob/main/docs/technology-design-a5b8129.md](https://github.com/SAP-docs/btp-developer-guide/blob/main/docs/technology-design-a5b8129.md)
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- UX Design: [https://github.com/SAP-docs/btp-developer-guide/blob/main/docs/user-experience-design-323bd93.md](https://github.com/SAP-docs/btp-developer-guide/blob/main/docs/user-experience-design-323bd93.md)
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