giuseppe-trisciuoglio/spring-data-neo4j

Spring Data Neo4j Integration Patterns

Overview

Provides Spring Data Neo4j integration patterns for Spring Boot applications. Covers node entity mapping with @Node and @Relationship, repository configuration (imperative and reactive), custom Cypher queries with @Query, and integration testing with embedded Neo4j databases.

When to Use

Use this skill when working with:

• Graph databases and Neo4j integration in Spring Boot
• Node entities, relationships, and Cypher queries
• Spring Data Neo4j repositories (imperative or reactive)
• Neo4j testing with embedded databases

Instructions

1. Set Up Spring Data Neo4j

Add the dependency:

Maven:

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

Gradle:

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

Configure connection in application.properties:

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

Configure Cypher-DSL dialect (recommended):

@Configuration
public class Neo4jConfig {
    @Bean
    Configuration cypherDslConfiguration() {
        return Configuration.newConfig()
            .withDialect(Dialect.NEO4J_5).build();
    }
}

Validation Checkpoint: Run MATCH (n) RETURN count(n) via cypher-shell to verify the connection works before proceeding.

2. Define Node Entities

1. Use @Node annotation to mark entity classes
2. Choose ID strategy:
   • Business key as @Id (immutable, natural identifier)
   • Generated @Id @GeneratedValue (Neo4j internal ID)
3. Define relationships with @Relationship annotation
4. Keep entities immutable with final fields
5. Use @Property for custom property names

Validation Checkpoint: If entity save fails, check for constraint violations—duplicate IDs violate uniqueness constraints.

3. Create Repositories

1. Extend repository interface:
   • Neo4jRepository<Entity, ID> for imperative operations
   • ReactiveNeo4jRepository<Entity, ID> for reactive operations
2. Use query derivation for simple queries
3. Apply @Query annotation for complex Cypher queries
4. Use $paramName syntax for parameters

Validation Checkpoint: Test repository with findAll() first—if empty, verify the Neo4j instance is running and credentials are correct.

4. Test Your Implementation

1. Use @DataNeo4jTest for repository testing with test slicing
2. Set up Neo4j Harness with embedded database and fixtures
3. Provide test data via withFixture() Cypher queries
4. Clean up test data between tests

Validation Checkpoint: If tests fail with "Connection refused", ensure the embedded Neo4j started successfully in @BeforeAll.

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

Example 1: Saving and Retrieving Entities

Input:

MovieEntity movie = new MovieEntity("The Matrix", "Welcome to the Real World", 1999);
movieRepository.save(movie);

MovieEntity found = movieRepository.findOneByTitle("The Matrix");

Output:

MovieEntity{
    title="The Matrix",
    description="Welcome to the Real World",
    year=1999,
    actorsAndRoles=[],
    directors=[]
}

Example 2: Custom Cypher Query

Input:

List<Book> books = authorRepository.findBooksAfterYear("J.R.R. Tolkien", 1950);

Output:

[
    Book{isbn="978-0547928210", name="The Fellowship of the Ring", year=1954},
    Book{isbn="978-0547928203", name="The Two Towers", year=1956},
    Book{isbn="978-0547928227", name="The Return of the King", year=1957}
]

Example 3: Relationship Traversal

Input:

@Query("MATCH (m:Movie)<-[:ACTED_IN]-(a:Person) " +
       "WHERE m.title = $title RETURN a.name as actorName")
List<String> findActorsByMovieTitle(@Param("title") String title);

List<String> actors = movieRepository.findActorsByMovieTitle("The Matrix");

Output:

["Keanu Reeves", "Laurence Fishburne", "Carrie-Anne Moss", "Hugo Weaving"]

---

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

See examples 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

Constraints and Warnings

• Do not mix imperative and reactive repositories in the same application.
• Neo4j transactions are required for write operations; ensure @Transactional is properly configured.
• Be cautious with deep relationship traversal as it can cause performance issues.
• Large result sets should be paginated to avoid memory problems.
• Cypher queries are case-sensitive; ensure consistent casing in property names.
• Immutable entities require proper wither methods for generated IDs.
• Relationships in Spring Data Neo4j are not lazy-loaded by default; consider projection for large graphs.
• The Neo4j Java driver is not compatible with reactive streams; use the reactive driver for reactive operations.

Troubleshooting

| Problem | Cause | Solution | |---------|-------|----------| | Connection refused on localhost:7687 | Neo4j server not running | Start Neo4j or use embedded Neo4j for tests | | Authentication failed | Wrong credentials | Check spring.neo4j.authentication.username/password | | Entity not saved / MATCH returns nothing | Transaction not committed | Add @Transactional or verify auto-commit settings | | ConstraintViolationException on save | Duplicate @Id value | Ensure IDs are unique or use @GeneratedValue | | Relationships missing in results | Wrong @Relationship direction | Check Direction.INCOMING/OUTGOING/UNDIRECTED | | @Query returns wrong data | Cypher parameter syntax | Use $paramName not $ {paramName} | | Test fails with @DataNeo4jTest | Embedded Neo4j not started | Ensure @BeforeAll starts Neo4j before tests |

References

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

• Annotations Reference
• Cypher Query Language
• Configuration Properties
• Repository Methods
• Projections and DTOs
• Transaction Management
• Performance Tuning

External Resources

• Spring Data Neo4j Official Documentation
• Neo4j Developer Guide
• Spring Data Commons Documentation