spring-data-neo4j

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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:

xml

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

Gradle:

groovy

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

Configure connection in application.properties:

properties

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

Configure Cypher-DSL dialect (recommended):

java

@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

java

@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

java

@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

java

@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

java

@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

java

@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:

java

@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:

java

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

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

Output:

java

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

Example 2: Custom Cypher Query

Input:

java

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

Output:

java

[
    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:

java

@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:

java

["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: