spring-data-neo4j

# Spring Data Neo4j Integration Patterns

## When to Use This Skill

To use this skill when you need to:
- Set up Spring Data Neo4j in a Spring Boot application
- Create and map graph node entities and relationships
- Implement Neo4j repositories with custom queries
- Write Cypher queries using @Query annotations
- Configure Neo4j connections and dialects
- Test Neo4j repositories with embedded databases
- Work with both imperative and reactive Neo4j operations
- Map complex graph relationships with bidirectional or unidirectional directions
- Use Neo4j's internal ID generation or custom business keys

## Overview

Spring Data Neo4j provides three levels of abstraction for Neo4j integration:
- **Neo4j Client**: Low-level abstraction for direct database access
- **Neo4j Template**: Medium-level template-based operations
- **Neo4j Repositories**: High-level repository pattern with query derivation

Key features include reactive and imperative operation modes, immutable entity mapping, custom query support via @Query annotation, Spring's Conversion Service integration, and full support for graph relationships and traversals.

## Quick Setup

### Dependencies

**Maven:**

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-neo4j</artifactId>
</dependency>

**Gradle:**

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-neo4j'
}

### Configuration

**application.properties:**

spring.neo4j.uri=bolt://localhost:7687
spring.neo4j.authentication.username=neo4j
spring.neo4j.authentication.password=secret

**Configure Neo4j Cypher-DSL Dialect:**

@Configuration
public class Neo4jConfig {

    @Bean
    Configuration cypherDslConfiguration() {
        return Configuration.newConfig()
            .withDialect(Dialect.NEO4J_5).build();
    }
}

## Basic Entity Mapping

### Node Entity with Business Key

@Node("Movie")
public class MovieEntity {

    @Id
    private final String title;  // Business key as ID

    @Property("tagline")
    private final String description;

    private final Integer year;

    @Relationship(type = "ACTED_IN", direction = Direction.INCOMING)
    private List<Roles> actorsAndRoles = new ArrayList<>();

    @Relationship(type = "DIRECTED", direction = Direction.INCOMING)
    private List<PersonEntity> directors = new ArrayList<>();

    public MovieEntity(String title, String description, Integer year) {
        this.title = title;
        this.description = description;
        this.year = year;
    }
}

### Node Entity with Generated ID

@Node("Movie")
public class MovieEntity {

    @Id @GeneratedValue
    private Long id;

    private final String title;

    @Property("tagline")
    private final String description;

    public MovieEntity(String title, String description) {
        this.id = null;  // Never set manually
        this.title = title;
        this.description = description;
    }

    // Wither method for immutability with generated IDs
    public MovieEntity withId(Long id) {
        if (this.id != null && this.id.equals(id)) {
            return this;
        } else {
            MovieEntity newObject = new MovieEntity(this.title, this.description);
            newObject.id = id;
            return newObject;
        }
    }
}

## Repository Patterns

### Basic Repository Interface

@Repository
public interface MovieRepository extends Neo4jRepository<MovieEntity, String> {

    // Query derivation from method name
    MovieEntity findOneByTitle(String title);

    List<MovieEntity> findAllByYear(Integer year);

    List<MovieEntity> findByYearBetween(Integer startYear, Integer endYear);
}

### Reactive Repository

@Repository
public interface MovieRepository extends ReactiveNeo4jRepository<MovieEntity, String> {

    Mono<MovieEntity> findOneByTitle(String title);

    Flux<MovieEntity> findAllByYear(Integer year);
}

**Imperative vs Reactive:**
- Use Neo4jRepository for blocking, imperative operations
- Use ReactiveNeo4jRepository for non-blocking, reactive operations
- **Do not mix imperative and reactive in the same application**
- Reactive requires Neo4j 4+ on the database side

## Custom Queries with @Query

@Repository
public interface AuthorRepository extends Neo4jRepository<Author, Long> {

    @Query("MATCH (b:Book)-[:WRITTEN_BY]->(a:Author) " +
           "WHERE a.name = $name AND b.year > $year " +
           "RETURN b")
    List<Book> findBooksAfterYear(@Param("name") String name,
                                   @Param("year") Integer year);

    @Query("MATCH (b:Book)-[:WRITTEN_BY]->(a:Author) " +
           "WHERE a.name = $name " +
           "RETURN b ORDER BY b.year DESC")
    List<Book> findBooksByAuthorOrderByYearDesc(@Param("name") String name);
}

**Custom Query Best Practices:**
- Use $parameterName for parameter placeholders
- Use @Param annotation when parameter name differs from method parameter
- MATCH specifies node patterns and relationships
- WHERE filters results
- RETURN defines what to return

## Testing Strategies

### Neo4j Harness for Integration Testing

**Test Configuration:**

@DataNeo4jTest
class BookRepositoryIntegrationTest {

    private static Neo4j embeddedServer;

    @BeforeAll
    static void initializeNeo4j() {
        embeddedServer = Neo4jBuilders.newInProcessBuilder()
            .withDisabledServer()  // No HTTP access needed
            .withFixture(
                "CREATE (b:Book {isbn: '978-0547928210', " +
                "name: 'The Fellowship of the Ring', year: 1954})" +
                "-[:WRITTEN_BY]->(a:Author {id: 1, name: 'J. R. R. Tolkien'}) " +
                "CREATE (b2:Book {isbn: '978-0547928203', " +
                "name: 'The Two Towers', year: 1956})" +
                "-[:WRITTEN_BY]->(a)"
            )
            .build();
    }

    @AfterAll
    static void stopNeo4j() {
        embeddedServer.close();
    }

    @DynamicPropertySource
    static void neo4jProperties(DynamicPropertyRegistry registry) {
        registry.add("spring.neo4j.uri", embeddedServer::boltURI);
        registry.add("spring.neo4j.authentication.username", () -> "neo4j");
        registry.add("spring.neo4j.authentication.password", () -> "null");
    }

    @Autowired
    private BookRepository bookRepository;

    @Test
    void givenBookExists_whenFindOneByTitle_thenBookIsReturned() {
        Book book = bookRepository.findOneByTitle("The Fellowship of the Ring");
        assertThat(book.getIsbn()).isEqualTo("978-0547928210");
    }
}

## Examples

Progress from basic to advanced examples covering complete movie database, social network patterns, e-commerce product catalogs, custom queries, and reactive operations.

See [examples](./references/examples.md) for comprehensive code examples.

## Best Practices

### Entity Design
- Use immutable entities with final fields
- Choose between business keys (@Id) or generated IDs (@Id @GeneratedValue)
- Keep entities focused on graph structure, not business logic
- Use proper relationship directions (INCOMING, OUTGOING, UNDIRECTED)

### Repository Design
- Extend Neo4jRepository for imperative or ReactiveNeo4jRepository for reactive
- Use query derivation for simple queries
- Write custom @Query for complex graph patterns
- Don't mix imperative and reactive in same application

### Configuration
- Always configure Cypher-DSL dialect explicitly
- Use environment-specific properties for credentials
- Never hardcode credentials in source code
- Configure connection pooling based on load

### Testing
- Use Neo4j Harness for integration tests
- Provide test data via withFixture() Cypher queries
- Use @DataNeo4jTest for test slicing
- Test both successful and edge-case scenarios

### Architecture
- Use constructor injection exclusively
- Separate domain entities from DTOs
- Follow feature-based package structure
- Keep domain layer framework-agnostic

### Security
- Use Spring Boot property overrides for credentials
- Configure proper authentication and authorization
- Validate input parameters in service layer
- Use parameterized queries to prevent Cypher injection

## References

For detailed documentation including complete API reference, Cypher query patterns, and configuration options:

- [Annotations Reference](./references/reference.md#annotations-reference)
- [Cypher Query Language](./references/reference.md#cypher-query-language)
- [Configuration Properties](./references/reference.md#configuration-properties)
- [Repository Methods](./references/reference.md#repository-methods)
- [Projections and DTOs](./references/reference.md#projections-and-dtos)
- [Transaction Management](./references/reference.md#transaction-management)
- [Performance Tuning](./references/reference.md#performance-tuning)

### External Resources
- [Spring Data Neo4j Official Documentation](https://docs.spring.io/spring-data/neo4j/reference/)
- [Neo4j Developer Guide](https://neo4j.com/developer/)
- [Spring Data Commons Documentation](https://docs.spring.io/spring-data/commons/reference/)