spring-boot-data-ddd

# 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** → Extend `AbstractAggregateRoot<T>` for domain events
2. **Map value objects** → Use `@Embedded` or `@Converter` for immutability
3. **Create repository interface** → One per aggregate root, extend appropriate base
4. **Implement service layer** → `@Transactional` on public methods, one aggregate per transaction
5. **Add projections** → Interface or record-based for read operations

## Quick Patterns

See [EXAMPLES.md](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 interfa