jpa - 有没有办法通过 QueryDSL 中的谓词 API 急切地获取惰性关系？

Question

我正在使用QueryDslPredicateExecutorSpring Data JPA 项目，并且我面临着急切获取惰性关系的需要。我知道我可以在 Repository 接口中使用本机 JPA-QL 查询，甚至可以使用 Query DSL 中的 JPAQLQuery，但我很感兴趣，如果这甚至可以方便地构建查询以满足未来的需求。

Answer 1

我有一个类似的问题，我必须在使用 Predicates 和 QueryDslPredicateExecutor 时获取加入集合。

我所做的是创建一个自定义存储库实现以添加一个允许我定义应该获取的实体的方法。

不要被这里的代码量吓倒，它实际上非常简单，您只需要做很少的更改即可在您的应用程序中使用它

这是自定义仓库的界面

@NoRepositoryBean
public interface JoinFetchCapableRepository<T, ID extends Serializable> extends     JpaRepository<T, ID>, QueryDslPredicateExecutor<T> {

    Page<T> findAll(Predicate predicate, Pageable pageable, JoinDescriptor... joinDescriptors);
}

连接描述符

public class JoinDescriptor {
    public final EntityPath path;
    public final JoinType type;

    private JoinDescriptor(EntityPath path, JoinType type) {
        this.path = path;
        this.type = type;
    }

    public static JoinDescriptor innerJoin(EntityPath path) {
        return new JoinDescriptor(path, JoinType.INNERJOIN);
    }

    public static JoinDescriptor join(EntityPath path) {
        return new JoinDescriptor(path, JoinType.JOIN);
    }

    public static JoinDescriptor leftJoin(EntityPath path) {
        return new JoinDescriptor(path, JoinType.LEFTJOIN);
    }

    public static JoinDescriptor rightJoin(EntityPath path) {
        return new JoinDescriptor(path, JoinType.RIGHTJOIN);
    }

    public static JoinDescriptor fullJoin(EntityPath path) {
        return new JoinDescriptor(path, JoinType.FULLJOIN);
    }
}

自定义存储库的实现

public class JoinFetchCapableRepositoryImpl <T, ID extends Serializable> extends QueryDslJpaRepository<T, ID> implements JoinFetchCapableRepository<T, ID> {

    private static final EntityPathResolver DEFAULT_ENTITY_PATH_RESOLVER = SimpleEntityPathResolver.INSTANCE;

    private final EntityPath<T> path;
    private final PathBuilder<T> builder;
    private final Querydsl querydsl;

    public JoinFetchCapableRepositoryImpl(JpaEntityInformation<T, ID> entityInformation, EntityManager entityManager) {
        this(entityInformation, entityManager, DEFAULT_ENTITY_PATH_RESOLVER);
    }

    public JoinFetchCapableRepositoryImpl(JpaEntityInformation<T, ID> entityInformation, EntityManager entityManager, EntityPathResolver resolver) {
        super(entityInformation, entityManager, resolver);
        this.path = resolver.createPath(entityInformation.getJavaType());
        this.builder = new PathBuilder<>(path.getType(), path.getMetadata());
        this.querydsl = new Querydsl(entityManager, builder);
    }

    @Override
    public Page<T> findAll(Predicate predicate, Pageable pageable, JoinDescriptor... joinDescriptors) {
        JPQLQuery countQuery = createQuery(predicate);
        JPQLQuery query = querydsl.applyPagination(pageable, createFetchQuery(predicate, joinDescriptors));

        Long total = countQuery.count();
        List<T> content = total > pageable.getOffset() ? query.list(path) : Collections.<T> emptyList();

        return new PageImpl<>(content, pageable, total);
    }

    protected JPQLQuery createFetchQuery(Predicate predicate, JoinDescriptor... joinDescriptors) {
        JPQLQuery query = querydsl.createQuery(path);
        for(JoinDescriptor joinDescriptor: joinDescriptors)
            join(joinDescriptor, query);
        return query.where(predicate);
    }

    private JPQLQuery join(JoinDescriptor joinDescriptor, JPQLQuery query) {
        switch(joinDescriptor.type) {
            case DEFAULT:
                throw new IllegalArgumentException("cross join not supported");
            case INNERJOIN:
                query.innerJoin(joinDescriptor.path);
                break;
            case JOIN:
                query.join(joinDescriptor.path);
                break;
            case LEFTJOIN:
                query.leftJoin(joinDescriptor.path);
                break;
            case RIGHTJOIN:
                query.rightJoin(joinDescriptor.path);
                break;
            case FULLJOIN:
                query.fullJoin(joinDescriptor.path);
                break;
        }
        return query.fetch();
    }
}

工厂创建自定义存储库，替换默认的 QueryDslJpaRepository

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

    protected RepositoryFactorySupport createRepositoryFactory(EntityManager entityManager) {

        return new JoinFetchCapableQueryDslJpaRepositoryFactory(entityManager);
    }
    private static class JoinFetchCapableQueryDslJpaRepositoryFactory<T, I extends Serializable> extends JpaRepositoryFactory {

        private EntityManager entityManager;

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

        protected Object getTargetRepository(RepositoryMetadata metadata) {
            return new JoinFetchCapableRepositoryImpl<>(getEntityInformation(metadata.getDomainType()), entityManager);
        }

        protected Class<?> getRepositoryBaseClass(RepositoryMetadata metadata) {
            return JoinFetchCapableRepository.class;
        }
    }
}

最后一步是更改 jpa 配置，使其使用此工厂而不是默认工厂：

<jpa:repositories base-package="com.mycompany.repository"
                      entity-manager-factory-ref="entityManagerFactory"
                      factory-class="com.mycompany.utils.spring.data.JoinFetchCapableQueryDslJpaRepositoryFactoryBean" />

然后你可以像这样从你的服务层使用它：

public Page<ETicket> list(ETicketSearch eTicket, Pageable pageable) {
    return eticketRepository.findAll(like(eTicket), pageable, JoinDescriptor.leftJoin(QETicket.eTicket.order));
}

通过使用 JoinDescriptor，您将能够根据您的服务需求指定要加入的内容。

由于 Murali 在这里的响应，我能够做到这一点：Spring Data JPA 和 Querydsl 使用 bean/constructor projection 获取列的子集请看一看。

Answer 2

Spring data引入了 JPA Entity Graph 支持。请注意，目前不适用于通过 EmbeddedIds 遍历的图。