Agent skill

spring-boot-data-ddd

Spring Boot 4 data layer implementation for Domain-Driven Design. Use when implementing JPA or JDBC aggregates, Spring Data repositories, transactional services, projections, or entity auditing. Covers aggregate roots with AbstractAggregateRoot, value object mapping, EntityGraph for N+1 prevention, and Spring Boot 4 specifics (JSpecify null-safety, AOT repositories). For DDD concepts and design decisions, see the domain-driven-design skill.

View SKILL.md on GitHub Repository
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npx add-skill https://github.com/joaquimscosta/arkhe-claude-plugins/tree/main/plugins/spring-boot/skills/spring-boot-data-ddd

SKILL.md

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

  1. 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: @NullMarked and @Nullable annotations
  • AOT Repository Compilation: Enabled by default for faster startup
  • Jakarta EE 11: All imports use jakarta.* namespace
  • ListCrudRepository: New interface returning List<T> instead of Iterable<T>

ListCrudRepository (Spring Data 3.1+)

New repository interface returning List<T> for better API ergonomics:

java
// 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

  1. One aggregate per transaction — Cross-aggregate changes via domain events
  2. Repository per aggregate root — Never for child entities
  3. Value objects are immutable — No setters, return new instances
  4. Flush before events — Call repository.save() before events dispatch
  5. Test with @DataJpaTest — Use TestEntityManager for setup

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