Child.java

@Table
@Value
@Builder(toBuilder = true)
public class Child {

    @Id
    private int id;
    private int parentId;
    private String name;
    private String path;
    List<GrandChild> grandChildList;


}

ChildRepository.java

@Repository
public interface ChildRepository extends ReactiveCrudRepository<Child, Integer> {

    @Query("select id,parent_id,name,path from child ")
    Flux<Child>findAll();

    @Query("select id,parent_id,name,path from child where parent_id = :parent_id ")
    Flux<Child> findAllByParentId(@Param("parent_id")final Integer parentId);
}

FamilyService.java

@Component
@Slf4j
public class FamilyService {

    @Autowired
    private ParentRepository parentRepository;

    @Autowired
    private ChildRepository childRepository;

    @Autowired
    private GrandChildRepository grandChildRepository;

    public Flux<Parent> getAllParents() {
        return parentRepository.findAll();
    }

    public Mono<List<Child>> getAllChildsList(final Integer parentId) {
        return childRepository.findAllByParentId(parentId).collectList();
    }

    public Flux<GrandChild> getGrandKids(final Integer childId) {
        return grandChildRepository.findAllByChildId(childId);
    }

    public Mono<List<GrandChild>> getGrandKidsList(final Integer childId) {
        return grandChildRepository.findAllByChildId(childId).collectList();
    }

    private Mono<List<Child>> getChildsWithKids(final List<Child> childList) {
        return Flux.fromIterable(childList).flatMap(child ->
                Mono.zip(Mono.just(child), getGrandKidsList(child.getId()))
                        .map(tuple2 -> tuple2.getT1().toBuilder().grandChildList(tuple2.getT2()).build())
        ).collectList();
    }

    public Flux<Parent> getFamiliesHierarchy() {

        return getAllParents()
                .flatMap(parent ->
                        getAllChildsList(parent.getId())
                                .flatMap(childList -> getChildsWithKids(childList))
                                .map(childList ->
                                        parent.toBuilder().childList(childList).build()
                                )

                );
    }

}

FamilyTreeController.java

@RestController
@Slf4j
public class FamilyTreeController {

    @Autowired
    private FamilyService familyService;

    @GetMapping("/v1/families")
    public Flux<Parent> viewAllParents() {
        return familyService.getFamiliesHierarchy();
    }

}

GrandChild

@Table
@Value
@Builder(toBuilder = true)
public class GrandChild {

    @Id
    private int id;
    private int childId;
    private String name;
    private String path;

}

GrandChildRepository.java

@Repository
public interface GrandChildRepository extends ReactiveCrudRepository<GrandChild, Integer> {

    @Query("select id,child_id,name,path from grand_child")
    Flux<GrandChild> findAll();

    @Query("select id,child_id,name,path from grand_child where child_id = :child_id ")
    Flux<GrandChild> findAllByChildId(@Param("child_id") final Integer childId);
}

Parent

@Table
@Value
@Builder(toBuilder = true)
public class Parent {

    @Id
    private int id;
    private String name;
    private String path;
    List<Child> childList;

}

ParentRepository.java

@Repository
public interface ParentRepository extends ReactiveCrudRepository<Parent, Integer> {

}

Schema Creation and Sample Data

create table if not exists parent
(
	id serial
		constraint parent_pk
			primary key,
	name varchar(255) not null,
	path varchar(255) not null
);

create table if not exists child
(
	id serial
		constraint child_pk
			primary key,
	parent_id integer not null
		constraint fk_parent_id
			references parent,
	name varchar(255) not null,
	path varchar(255) not null
);

create table if not exists grand_child
(
	id serial
		constraint grand_child_pk
			primary key,
	child_id integer not null
		constraint fk_child_id
			references child,
	name varchar(255) not null,
	path varchar(255)
);

 

-- Sample Data -- 

INSERT INTO public.parent(id, name, path) VALUES (1,'William Rockefeller Sr.','1');
INSERT INTO public.parent(id, name, path) VALUES (2,'George H. W. Bush','2');
INSERT INTO public.parent(id, name, path) VALUES (3,'Obama','3');

insert into public.child(id, parent_id, name, path) VALUES (1,1,'John D. Rockefeller','1.1')
insert into public.child(id, parent_id, name, path) VALUES (2,1,'William Rockefeller','1.2');
insert into public.child(id, parent_id, name, path) VALUES (3,1,'Frank Rockefeller','1.3');
insert into public.child(id, parent_id, name, path) VALUES (4,2,'George W Bush','2.1');
insert into public.child(id, parent_id, name, path) VALUES (5,2,'Jeb Bush','2.2');
insert into public.child(id, parent_id, name, path) VALUES (6,3,'Malia Obama','3.1');
insert into public.child(id, parent_id, name, path) VALUES (7,3,'Sasha Obama','3.2');

INSERT INTO public.grand_child (id, child_id, name, path) VALUES (1, 1, 'Elizabeth', '1.1.1');
INSERT INTO public.grand_child (id, child_id, name, path) VALUES (2, 1, 'ALta', '1.1.2');
INSERT INTO public.grand_child (id, child_id, name, path) VALUES (3, 1, 'Edith', '1.1.3');
INSERT INTO public.grand_child (id, child_id, name, path) VALUES (4, 2, 'Godfrey', '1.2.1');
INSERT INTO public.grand_child (id, child_id, name, path) VALUES (5, 2, 'James', '1.2.2');
INSERT INTO public.grand_child (id, child_id, name, path) VALUES (6, 2, 'Isabel', '1.2.3');
INSERT INTO public.grand_child (id, child_id, name, path) VALUES (7, 4, 'Barbara Bush', '2.1.1');
INSERT INTO public.grand_child (id, child_id, name, path) VALUES (8, 4, 'Jenna Bush', '2.1.2');
INSERT INTO public.grand_child (id, child_id, name, path) VALUES (9, 5, 'Noel Bush', '2.2.1');
INSERT INTO public.grand_child (id, child_id, name, path) VALUES (10, 5, 'Jebby Bush', '2.2.2');