JPA Specification sort by native SQL field - spring

Question

I'm using Spring Boot v1.5.3
In my code, I have a search operation with a lot of conditions.
public Page<ParentObject> search(Pageable pageable) {
Specification<ParentObject> specification = (root, cq, cb) -> {
Predicate p = cb.and(
cb.equals(root.get("child").get("id"), "someValue"),
// a lot of predicates appended by conditions
);
return p;
};
Sort newSort = pageable.getSort().and(new Sort(Sort.Direction.ASC, "child.id"));
pageable = new PageRequest(pageable.getPageNumber(), pageable.getPageSize(), newSort)
Page<ParentObject> result = parentObjectRepository.findAll(specification, pageable);
return result;
}
The problem is that my parent table contains child_id field with index. And I want SQL to be like:
SELECT .... FROM parent p INNER JOIN child c ON c.id = p.child_id WHERE ...
ORDER BY p.child_id ASC;
But in result I have:
SELECT .... FROM parent p INNER JOIN child c ON c.id = p.child_id WHERE ...
ORDER BY c.id ASC;
Pay attention to ORDER BY clause. If I have c.id index is not involved and the search is slow. If I have ORDER BY p.child_id it works much faster.
I tried to use
Sort newSort = pageable.getSort().and(new Sort(Sort.Direction.ASC, "child"));
but it does not work as expected.
Entity:
public class ParentObject {
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "child_id", referencedColumnName = "id")
private ChildObject child;
}
I can't replace this by native SQL, because this search specification contains 30+ if/else statements and it will take a lot of time to rewrite the code.
How can I solve this problem? Thanks in advance for your answers.

Answer 1

Finally, I found a solution. As we know, ORM works with database thru entities.
All my entities have String (UUID) values as ids. So, I have added the following code into my ParentObject:
public class ParentObject {
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "child_id", referencedColumnName = "id")
private ChildObject child;
#Column(name = "child_id", insertable = false, updatable = false)
private String childId;
}
As you see, here I have added simple field that contains id of child object. It's important to mark this field as insertable = false, updatable = false and we can't change this field in the code, this is read-only field. But this allows us to sort results by parent.child_id, not by child.id. If we need to replace child object, need just call setChild(newValue).
And finally, my search method now looks like:
public Page<ParentObject> search(Pageable pageable) {
Specification<ParentObject> specification = (root, cq, cb) -> {
Predicate p = cb.and(
cb.equals(root.get("child").get("id"), "someValue"),
// a lot of predicates appended by conditions
);
return p;
};
// IMPORTANT change in next line
Sort newSort = pageable.getSort().and(new Sort(Sort.Direction.ASC, "childId"));
pageable = new PageRequest(pageable.getPageNumber(), pageable.getPageSize(), newSort)
Page<ParentObject> result = parentObjectRepository.findAll(specification, pageable);
return result;
}
And in result I have the following SQL query:
SELECT .... FROM parent p INNER JOIN child c ON c.id = p.child_id WHERE ...
ORDER BY p.child_id ASC;
Hope this would be useful for someone