how to select multiple objects in spring data jpa using specifications - spring-data-jpa

Question

I have following #Query, that is perfectly working fine. But now I have a scenario where there screen needs a filter, that will add some where clauses to the query.
#Query
("
SELECT
ef, ed, ea
FROM EntityA ea
JOIN EntityB eb
JOIN EntityC ec
JOIN EntityD ed
JOIN EntityE ee
JOIN EntityF ef
WHERE
TRUNC(ee.date) = TRUNC(:date)
-- conditions based on screen filter parameters
AND ef.amount = :amount
AND LOWER(ec.name) LIKE LOWER('%' || :name || '%')
AND ec.projectId = :projectId
AND ed.divisionId = :divisionId
")
Found that there is a good Specifications support to dynamically create the queries as per requirement.
But not sure how do I select multiple objects ef, ed & ea in one go using Specifications, otherwise I have to write 4 more queries to return result based on filter criteria.
N.B. Not using eager loading for performance reasons as entities are used by multiple services.

Answer 1

Specifications are only used for dynamically creating a where clause.
If you also need to control the select clause I recommend using the JPA Criteria API inside a custom method of your repository.

Answer 2

I was able to achieve this by implementing Custom Repositories, auto-wiring the EntityManager in that implementation class and then building the final JPQL based on parameters passed. A good example is in Eugen's blog.
Previously I had following structure
public interface EntityARepository extends JpaRepository<EntityA, Long> {
#Query(...)
List<EntityA> findAllBy(Date filterDate, Long amount, String name, Long projectId, Long divisionId);
}
public interface EntityAService {
List<Object[]> findAllBy(Date filterDate, Long amount, String name, Long projectId, Long divisionId);
}
#Service
public class EntityAServiceImpl implements EntityAService {
#Autowired
EntityARepository entityARepository;
#Override
public List<Object[]> findAllBy(Date filterDate, Long amount, String name, Long projectId, Long divisionId) {
...
...
...
}
}
And by using Custom Repositories all becomes like
public interface EntityACustomRepository {
List<Object[]> findAllBy(Date filterDate, Long amount, String name, Long projectId, Long divisionId);
}
public interface EntityARepository extends JpaRepository<EntityA, Long> {
//#Query(...)
//List<EntityA> findAllBy(Date filterDate, Long amount, String name, Long projectId, Long divisionId);
}
#Repository
public class EntityACustomRepositoryImpl implements EntityACustomRepository {
// autowiring entityManager helped to create and execute dynamic jpql
#Autowired
EntityManager entityManager;
public List<Object[]> findAllBy(Date filterDate, Long amount, String name, Long projectId, Long divisionId) {
String jpql = "SELECT " +
" ef, ed, ea " +
" FROM EntityA ea " +
" JOIN EntityB eb " +
" JOIN EntityC ec " +
" JOIN EntityD ed " +
" JOIN EntityE ee " +
" JOIN EntityF ef " +
" WHERE " +
" TRUNC(ee.date) = TRUNC(:date) "
;
//conditions based on screen filter parameters
if(amount!=null && amount>0L) {
jpql += " AND ef.amount = :amount ";
}
if(name!=null && name.trim().length()>0) {
jpql += " AND LOWER(ec.name) LIKE LOWER('%' || :name || '%') ";
}
if(projectId!=null && projectId>0L) {
jpql += " AND ec.projectId = :projectId ";
}
if(divisionId!=null && divisionId>0L) {
jpql += " AND ed.divisionId = :divisionId ";
}
Query query = entityManager.createQuery(jpql);
query.setParameter("date", filterDate);
if(amount!=null && amount>0L) {
query.setParameter("amount", amount);
}
if(name!=null && name.trim().length()>0) {
query.setParameter("name", name);
}
if(projectId!=null && projectId>0L) {
query.setParameter("projectId", projectId);
}
if(divisionId!=null && divisionId>0L) {
query.setParameter("divisionId", divisionId);
}
return query.getResultList();
}
}
public interface EntityAService {
List<Object[]> findAllBy(Date filterDate, Long amount, String name, Long projectId, Long divisionId);
}
#Service
public class EntityAServiceImpl implements EntityAService {
#Autowired
EntityARepository entityARepository;
#Override
public List<Object[]> findAllBy(Date filterDate, Long amount, String name, Long projectId, Long divisionId) {
return entityARepository.findAllBy(filterDate, amount, name, projectId, divisionId);
}
}

Answer 3

It is possible to query on child entities using the Specification API if you map them with JPA, e.g. with #OneToMany.
#Entity
#Table(...)
public class EntityA {
// Omitting fields
#OneToMany(...)
private List<EntityB> bList = new ArrayList<>();
}
public class EntityASpecification implements Specification<EntityA> {
private SearchCriteriaValueClass criteria;
public EntityASpecification(SearchCriteriaValueClass criteria) {
this.criteria = criteria;
}
#Override
public Predicate toPredicate(Root<EntityA> root, CriteriaQuery<?> query, CriteriaBuilder builder) {
ListJoin<EntityA, EntityB> pathToEntityB = root.join(EntityA_.bList, JoinType.INNER);
Predicate amountInBIsEqual = builder.equal(pathToEntityB.get(EntityB_.amount), criteria.getAmount);
Path<SomeEntityAField> pathToAField = root.get(EntityA_.someAField);
Predicate someValueInA = pathToAField.in(criteria.getCollectionForAFieldToBeIn());
query.distinct(true);
return builder.and(amountInBIsEqual, someValueInA);
}
}
Obviously a Specification is defined for one Entity and can only return instances of that. I don't see any (safe and effective) way of returning instances of F, D and A in one method call other than them being connected in a has-a relationship.