One To One Query in JPA springboot

 One To One Query in JPA springboot

In JPA and Spring Boot, you can perform a one-to-one query using JPQL (Java Persistence Query Language) or by using Spring Data JPA's query methods.

Assuming you have two entities, let's call them EntityA and EntityB, with a one-to-one relationship between them, you can write a JPQL query to retrieve EntityA and its associated EntityB as follows:

@Entity public class EntityA { @Id private Long id; @OneToOne(mappedBy = "entityA") private EntityB entityB; // ... } @Entity public class EntityB { @Id private Long id; @OneToOne @JoinColumn(name = "entity_a_id") private EntityA entityA; // ... }

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TypedQuery<EntityA> query = entityManager.createQuery(

    "SELECT a FROM EntityA a JOIN FETCH a.entityB b WHERE a.id = :id", EntityA.class);

query.setParameter("id", entityId);

EntityA entityA = query.getSingleResult();

Here, we are using the JOIN FETCH clause to fetch the associated EntityB eagerly. You can also use LEFT JOIN FETCH to retrieve EntityA even if it has no associated EntityB.

Alternatively, you can use Spring Data JPA's query methods to achieve the same result. For example:

public interface EntityARepository extends JpaRepository<EntityA, Long> { @Query("SELECT a FROM EntityA a JOIN FETCH a.entityB b WHERE a.id = :id") EntityA findOneWithEntityBById(Long id); }