joaquimscosta Spring Boot Data Layer for DDD
Implements DDD tactical patterns with Spring Data JPA and Spring Data JDBC in Spring Boot 4.
Technology Selection
| Choose | When |
|---|---|
| Spring Data JPA | Complex queries, existing Hibernate expertise, need lazy loading |
| Spring Data JDBC | DDD-first design, simpler mapping, aggregate-per-table, no lazy loading |
Spring Data JDBC enforces aggregate boundaries naturally—recommended for new DDD projects.
Core Workflow
- Define aggregate root → 2. Map value objects → 3. Create repository → 4. Implement service layer → 5. Add projections
See WORKFLOW.md for detailed step-by-step instructions with code examples.
Quick Patterns
See EXAMPLES.md for complete working examples including:
- Aggregate Root with AbstractAggregateRoot and domain events (Java + Kotlin)
- Repository with EntityGraph for N+1 prevention
- Transactional Service with proper boundaries
- Value Objects (Strongly-typed IDs, Money pattern)
- Projections for efficient read operations
- Auditing with automatic timestamps
Spring Boot 4 Specifics
- JSpecify null-safety:
@NullMarkedand@Nullableannotations - AOT Repository Compilation: Enabled by default for faster startup
- Jakarta EE 11: All imports use
jakarta.*namespace - ListCrudRepository: New interface returning
List<T>instead ofIterable<T>
ListCrudRepository (Spring Data 3.1+)
New repository interface returning List<T> for better API ergonomics:
// OLD: CrudRepository returns Iterable<T>
public interface UserRepository extends CrudRepository<User, Long> {
Iterable<User> findAll(); // Requires conversion to List
}
// NEW: ListCrudRepository returns List<T>
public interface UserRepository extends ListCrudRepository<User, Long> {
List<User> findAll(); // Direct List return
List<User> findAllById(Iterable<Long> ids); // Also List
}
// Can also extend both for full functionality
public interface UserRepository extends
ListCrudRepository<User, Long>,
ListPagingAndSortingRepository<User, Long> {
}
Benefits: No more StreamSupport.stream(iterable.spliterator(), false).toList() conversions.
Detailed References
- Workflow: See WORKFLOW.md for detailed step-by-step data layer implementation
- Examples: See EXAMPLES.md for complete working code examples
- Troubleshooting: See TROUBLESHOOTING.md for common issues and Boot 4 migration
- Aggregates & Entities: See references/AGGREGATES.md for complete patterns with value objects, typed IDs, auditing
- Repositories & Queries: See references/REPOSITORIES.md for custom queries, projections, specifications
- Transactions: See references/TRANSACTIONS.md for propagation, isolation, cross-aggregate consistency
Related Skills
| Need | Skill |
|---|---|
| DDD concepts and design | domain-driven-design |
| REST API for aggregates | spring-boot-web-api |
| Module boundaries | spring-boot-modulith |
| Repository testing | spring-boot-testing |
Anti-Pattern Checklist
| Anti-Pattern | Fix |
|---|---|
FetchType.EAGER on associations |
Use LAZY + @EntityGraph when needed |
| Returning entities from controllers | Convert to DTOs in service layer |
@Transactional on private methods |
Use public methods (proxy limitation) |
Missing readOnly = true on queries |
Add for read operations (performance) |
| Direct aggregate-to-aggregate references | Reference by ID only |
| Multiple aggregates in one transaction | Use domain events for eventual consistency |
Critical Reminders
- One aggregate per transaction — Cross-aggregate changes via domain events
- Repository per aggregate root — Never for child entities
- Value objects are immutable — No setters, return new instances
- Flush before events — Call
repository.save()before events dispatch - Test with
@DataJpaTest— UseTestEntityManagerfor setup