ShrimpPhaser ShrimpPhaser - 2 months ago 34
Java Question

Paging and sorting in Spring Data Neo4j 4

is there pagination support for custom queries in SDN4?


  • If yes, how does it work?

  • If no, is there a workarround?



I have the following Spring Data Neo4j 4 repository:

@Repository
public interface TopicRepository
extends GraphRepository<Topic>,IAuthorityLookup {

// other methods omitted
@Query("MATCH (t:Topic)-[:HAS_OFFICER]->(u:User) "
+ "WHERE t.id = {0} "
+ "RETURN u")
public Page<User> topicOfficers(Long topicId, Pageable pageable);
}


And the corresponding testcase:

@Test
public void itShouldReturnAllOfficersAsAPage() {
Pageable pageable = new PageRequest(1,10);
Page<User> officers = topicRepository.topicOfficers(1L, pageable);
assertNotNull(officers);
}


When I run the test, I run into the following exception

Failed to convert from type java.util.ArrayList<?> to type org.springframework.data.domain.Page<?> for value '[org.lecture.model.User@1]';
nested exception is org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type java.util.ArrayList<?> to type org.springframework.data.domain.Page<?>


This is my setup:

dependencies {
//other dependencies omitted
compile("org.neo4j:neo4j-cypher-dsl:2.0.1")


compile "org.neo4j.app:neo4j-server:2.2.2"

compile(group: 'org.springframework.data',
name: 'spring-data-neo4j',
version: '4.0.0.BUILD-SNAPSHOT')


compile(group: 'org.springframework.data',
name: 'spring-data-neo4j',
version: '4.0.0.BUILD-SNAPSHOT',
classifier: 'tests')

testCompile(group: 'org.neo4j',
name: 'neo4j-kernel',
version: '2.2.2',
classifier: 'tests')

testCompile(group: 'org.neo4j.app',
name: 'neo4j-server',
version: '2.2.2',
classifier: 'tests')

testCompile(group: 'org.neo4j',
name: 'neo4j-io',
version: '2.2.2',
classifier: 'tests')
}


The Snapshot I use should able to handle pagination, since the following test runs just fine:

@Test
public void itShouldReturnAllTopicsAsAPage() {

Pageable pageable = new PageRequest(1,10);
Page<Topic> topics = topicRepository.findAll(pageable);

assertNotNull(topics);
}

Answer

At the moment this isn't possible.

To enable this feature we'd need to do a few things. First at startup we would need to inspect the query's associated method signature and mark the query as requiring paging. Then at runtime when the method was invoked we'd need to obtain the pageable instance, extract the page parameters and apply them as SKIP and LIMIT clauses to the associated Cypher query. Finally, on return, we'd need wrap the results in a Page object. So there's a bit of work to be done to enable this.

In the meantime you could try adding the SKIP and LIMIT clauses with parameterised values to the query, and pass the appropriate values in via to the query method. I haven't tried this, but it should work - in theory:

  @Query("MATCH (t:Topic)-[:HAS_OFFICER]->(u:User) "
+ "WHERE t.id = {0} "
+ "RETURN  u SKIP {1} LIMIT {2}" )
public List<User> topicOfficers(long topicId, long skip, long limit)