Spring Data JPA+JpaSpecificationExecutor+EntityGraph

Question

（使用Spring Data JPA）我有两个实体父和子,它们之间具有一个或多个或多个双向关系。我将@NamedEntityGraph添加到父实体，如下所示：

@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，父级子级的fetch类型是lazy的。这是故意的。当我询问个别家长时，我不想总是急切地加载孩子。通常情况下，我可以使用我的命名实体图来按需加载孩子们。但是.....

有一个特定的情况，我想查询一个或多个家长和迫切加载他们的孩子。除此之外，我还需要能够以编程方式构建这个查询。spring数据提供了JpaSpecificationExecutor，它允许构建动态查询，但我不知道如何将它与实体图结合使用，以便在这种特定情况下快速加载子项。这有可能吗？是否有其他方法可以使用规范将“加载到”许多实体中？

Answer 1

null

@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，将此添加到配置中：

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

有关自定义存储库的更多信息:http://docs.spring.io/spring-data/jpa/docs/current/reference/html/#repositories.custom-behavior-for-all-repositories