Spring Data/JPS (N+1) SELECTs with OneToOne associations - spring

Question

In my Spring Data application I ran into (N+1) selects issue.
I have a following Spring Data entities:
#Entity
#Table(name = "card_categories")
public class CardCategory extends BaseEntity implements Serializable {
#Id
#SequenceGenerator(name = "card_categories_id_seq", sequenceName = "card_categories_id_seq", allocationSize = 1)
#GeneratedValue(strategy = GenerationType.AUTO, generator = "card_categories_id_seq")
private Long id;
private String name;
...
}
#Entity
#Table(name = "levels")
public class Level extends BaseEntity implements Serializable {
#Id
#SequenceGenerator(name = "levels_id_seq", sequenceName = "levels_id_seq", allocationSize = 1)
#GeneratedValue(strategy = GenerationType.AUTO, generator = "levels_id_seq")
private Long id;
private String name;
...
}
#Entity
#Table(name = "card_categories_levels")
public class CardCategoryLevel extends BaseEntity implements Serializable {
#Id
#SequenceGenerator(name = "card_categories_levels_id_seq", sequenceName = "card_categories_levels_id_seq", allocationSize = 1)
#GeneratedValue(strategy = GenerationType.AUTO, generator = "card_categories_levels_id_seq")
private Long id;
#OneToOne
#JoinColumn(name = "card_category_id")
private CardCategory cardCategory;
#OneToOne
#JoinColumn(name = "level_id")
private Level level;
...
}
and empty Spring Data repository:
#Repository
public interface CardCategoryLevelRepository extends JpaRepository<CardCategoryLevel, Long> {
}
When I try to fetch all CardCategoryLevel entities by cardCategoryLevelRepository.findAll() method it produces 3 SELECTs for an each row in my card_categories_levels table.
In order to use one single JOIN instead of N+1 SELECTs I have reimplemented my CardCategoryLevelRepository:
#Repository
public interface CardCategoryLevelRepository extends JpaRepository<CardCategoryLevel, Long> {
#Query(value = "SELECT ccl FROM CardCategoryLevel ccl LEFT JOIN FETCH ccl.cardCategory cc LEFT JOIN FETCH ccl.level l where cc = :cardCategory and l = :level")
CardCategoryLevel findByCardCategoryAndLevel(#Param("cardCategory") CardCategory cardCategory, #Param("level") Level level);
#Override
#Query(value = "SELECT ccl FROM CardCategoryLevel ccl LEFT JOIN FETCH ccl.cardCategory LEFT JOIN FETCH ccl.level")
List<CardCategoryLevel> findAll();
}
but I'm not sure I did it in a right optimal way.
Please validate my approach and tell it is optimal workaround for (N+1) SELECTs issue with OneToOne associations in Spring Data or no and what is the best way to solve it.
Should I leave it as is or may be move to some other abstraction.. for example like QueryDSL or something like that ?

Answer 1

Thanks to Xtreme Biker I have re-implemented my solution with entity graphs and QueryDSL