One To Many Query in JPA springboot

One To Many Query in JPA springboot

In JPA with Spring Boot, you can perform a one-to-many query using the JOIN FETCH clause in a JPQL (Java Persistence Query Language) query. This will allow you to retrieve a single entity and all of its associated child entities in a single database query.

Assuming you have an entity named Parent with a one-to-many relationship to Child, where Parent has a Set<Child> property, you can write a JPQL query like this:

SELECT p FROM Parent p JOIN FETCH p.children WHERE p.id = :parentId

This query will fetch a single Parent entity by its id and eagerly fetch all of its associated Child entities. You can then execute this query using a Spring Data JPA repository interface:

public interface ParentRepository extends JpaRepository<Parent, Long> { @Query("SELECT p FROM Parent p JOIN FETCH p.children WHERE p.id = :parentId") Parent findByIdWithChildren(@Param("parentId") Long parentId); }

You can then use this repository method to retrieve a Parent entity and its associated Child entities:

Parent parent = parentRepository.findByIdWithChildren(parentId); Set<Child> children = parent.getChildren();