spring-data-neo4j

SKILL.md

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

Use @Node annotation to mark entity classes

Choose ID strategy:

Business key as @Id (immutable, natural identifier)

Generated @Id @GeneratedValue (Neo4j internal ID)

Define relationships with @Relationship annotation

Keep entities immutable with final fields

Use @Property for custom property names

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

3. Create Repositories

Extend repository interface:

Neo4jRepository<Entity, ID> for imperative operations

ReactiveNeo4jRepository<Entity, ID> for reactive operations

Use query derivation for simple queries

Apply @Query annotation for complex Cypher queries

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

Use @DataNeo4jTest for repository testing with test slicing

Set up Neo4j Harness with embedded database and fixtures

Provide test data via withFixture() Cypher queries

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

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