Spring Data JPA + JpaSpecificationExecutor + EntityGraph

java spring jpa spring-data spring-data-jpa

2022-09-01 15:21:15

（使用弹簧数据JPA）我有两个实体，它们之间有一对多/多一双向关系。我向父实体添加一个@NamedEntityGraph，如下所示：ParentChild

@Entity
@NamedEntityGraph(name = "Parent.Offspring", attributeNodes = @NamedAttributeNodes("children"))
public class Parent{
//blah blah blah

@OneToMany(mappedBy = "parent", fetch = FetchType.LAZY)
Set<Child> children;

//blah blah blah
}

请注意，父项子项的读取类型是 LAZY。这是故意的。当我询问单个父母时，我并不总是想急于加载孩子。通常，我可以使用我的命名实体图来急切地按需加载孩子，可以这么说。但。。。。。

有一个特定的情况，我想查询一个或多个父母，并渴望加载他们的孩子。除此之外，我还需要能够以编程方式构建此查询。Spring Data提供了JpaSpecificationExecutor，它允许人们构建动态查询，但我无法弄清楚如何在这种特定情况下将其与实体图结合使用，以便预先加载子级。这有可能吗？有没有其他方法可以使用规范预先加载“toMany实体”？

答案 1

解决方案是创建一个实现以下功能的自定义存储库接口：

@NoRepositoryBean
public interface CustomRepository<T, ID extends Serializable> extends JpaRepository<T, ID>, JpaSpecificationExecutor<T> {

    List<T> findAll(Specification<T> spec, EntityGraphType entityGraphType, String entityGraphName);
    Page<T> findAll(Specification<T> spec, Pageable pageable, EntityGraphType entityGraphType, String entityGraphName);
    List<T> findAll(Specification<T> spec, Sort sort, EntityGraphType entityGraphType, String entityGraphName);
    T findOne(Specification<T> spec, EntityGraphType entityGraphType, String entityGraphName);

}

还要创建一个实现：

@NoRepositoryBean
public class CustomRepositoryImpl<T, ID extends Serializable> extends SimpleJpaRepository<T, ID> implements CustomRepository<T, ID> {

    private EntityManager em;

    public CustomRepositoryImpl(Class<T> domainClass, EntityManager em) {
        super(domainClass, em);
        this.em = em;
    }

    @Override
    public List<T> findAll(Specification<T> spec, EntityGraph.EntityGraphType entityGraphType, String entityGraphName) {
        TypedQuery<T> query = getQuery(spec, (Sort) null);
        query.setHint(entityGraphType.getKey(), em.getEntityGraph(entityGraphName));
        return query.getResultList();
    }

    @Override
    public Page<T> findAll(Specification<T> spec, Pageable pageable, EntityGraph.EntityGraphType entityGraphType, String entityGraphName) {
        TypedQuery<T> query = getQuery(spec, pageable.getSort());
        query.setHint(entityGraphType.getKey(), em.getEntityGraph(entityGraphName));
        return readPage(query, pageable, spec);
    }

    @Override
    public List<T> findAll(Specification<T> spec, Sort sort, EntityGraph.EntityGraphType entityGraphType, String entityGraphName) {
        TypedQuery<T> query = getQuery(spec, sort);
        query.setHint(entityGraphType.getKey(), em.getEntityGraph(entityGraphName));
        return query.getResultList();
    }

    @Override
    public T findOne(Specification<T> spec, EntityGraph.EntityGraphType entityGraphType, String entityGraphName) {
        TypedQuery<T> query = getQuery(spec, (Sort) null);
        query.setHint(entityGraphType.getKey(), em.getEntityGraph(entityGraphName));
        return query.getSingleResult();
    }
}

并创建一个工厂：

public class CustomRepositoryFactoryBean<R extends JpaRepository<T, I>, T, I extends Serializable> extends JpaRepositoryFactoryBean<R, T, I> {

    protected RepositoryFactorySupport createRepositoryFactory(EntityManager entityManager) {
        return new CustomRepositoryFactory(entityManager);
    }

    private static class CustomRepositoryFactory<T, I extends Serializable> extends JpaRepositoryFactory {

        private EntityManager entityManager;

        public CustomRepositoryFactory(EntityManager entityManager) {
            super(entityManager);
            this.entityManager = entityManager;
        }

        protected Object getTargetRepository(RepositoryMetadata metadata) {
            return new CustomRepositoryImpl<T, I>((Class<T>) metadata.getDomainType(), entityManager);
        }

        protected Class<?> getRepositoryBaseClass(RepositoryMetadata metadata) {
            // The RepositoryMetadata can be safely ignored, it is used by the JpaRepositoryFactory
            //to check for QueryDslJpaRepository's which is out of scope.
            return CustomRepository.class;
        }
    }

}

并将默认的存储库工厂bean更改为新的bean，例如，在spring boot中，将其添加到配置中：

@EnableJpaRepositories(
    basePackages = {"your.package"},
    repositoryFactoryBeanClass = CustomRepositoryFactoryBean.class
)

有关自定义存储库的详细信息：http://docs.spring.io/spring-data/jpa/docs/current/reference/html/#repositories.custom-behaviour-for-all-repositories

答案 2

我设法通过覆盖方法并添加注释来实现这一点：findAll@EntityGraph

public interface BookRepository extends JpaSpecificationExecutor<Book> {
   @Override
   @EntityGraph(attributePaths = {"book.author"})
   List<Book> findAll(Specification<Book> spec);
}