Spring mongodb how to use crudRespository with embedded documents - schema

Question

Why when I created crudRespository to do search on embedded object do none of the queries work and all of them return null. Is there something I'm doing wrong? There is an example.
I hope this is not a limitation of the spring mongodb. Maybe you know a different way to extract embedded object? I could use #DbRef but I read that it is not recommended for the performance issues.
Country.class
#Document(collection="countries")
#TypeAlias("ctry")
public class Country {
#Id private BigInteger id;
private String name;
private Continent continent;
public Country(String name, Continent continent) {
setName(name);
setContinent(continent);
}
//get/set omitted
}
Embedded document Continent.class
public final class Continent {
private final long id;
private final String name;
public Continent(long id, String name) {
this.id = id;
this.name = name;
}
//get/set omitted
}
ContinentRespository.class - this works fine the data is returned as it should
public interface CountryRepository extends Repository<Country, BigInteger> {
//------------------------------------------- equality
public Country findByName(String countryName);
#Query("{name : ?0}")
public Country findByNameQuery(String countryName);
}
ContinentRespository.class - all the methods always return null :/
public interface ContinentRepository extends CrudRepository<Continent, Long> {
public Continent findByName(String name);
#Query("{name : ?0}")
public Continent findByNameQuery(String name);
}
RespositoryTest.class - test class testFindEmbeddedContinent fails because returned object is null. testFindDocumentCountry works as expected
#ContextConfiguration(classes={MongoConfig.class})
#RunWith(SpringJUnit4ClassRunner.class)
public class RepositoryTest {
#Autowired private CountryRepository countryRepository;
#Autowired private ContinentRepository continentRepo;
#Autowired private MongoOperations mongoOps;
#Autowired private MongoTemplate template;
#Before
public void reset() {
DBCollection countries = template.getCollection("countries");
countries.drop();
countries.insert(dbObjectFromJson("{ '_id' : '8', '_class' : 'ctry', 'name' : 'Japan', 'continent' : { '_id' : 2, 'name' : 'Asia' } }"));
}
#Test
public void testFindEmbeddedContinent() {
Continent asia = continentRepo.findByName("Asia");
assertNotNull(asia);
assertThat(asia.getName(), is(equalTo("Asia")));
}
#Test
public void testFindDocumentCountry() {
Country japan = countryRepository.findByName("Japan");
assertNotNull(japan);
assertThat(japan.getContinent().getName(), is(equalTo("Asia")));
assertThat(japan.getName(), is(equalTo("Japan")));
}
private static DBObject dbObjectFromJson(String json) {
return (DBObject) JSON.parse(json);
}
}

Answer 1

A repository - by definition - mimics a collection of aggregate roots. In MongoDB this translates into top-level documents of a collection. Thus, you can only create repositories for top-level documents, i.e. Country in your case.
Im an not totally sure that it makes sense that a Continent is a property of a Country (as usually a country is part of a continent) but that might just be due to the sample. If you want to query Continents independently, make them a top-level document and keep references to the country either using simple ID or a DBRef (the former recommended).