spring-data-neo4j

---
name: spring-data-neo4j
description: Provides Spring Data Neo4j integration patterns for Spring Boot applications. Use when you need to work with a graph database, Neo4j nodes and relationships, Cypher queries, or Spring Data Neo4j. Creates node entities with @Node annotation, defines relationships with @Relationship, writes Cypher queries using @Query, configures imperative and reactive Neo4j repositories, implements graph traversal patterns, and sets up testing with embedded databases.
license: MIT
---

# 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

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

```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](./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

## 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](./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/)