Spring Data JPA和Querydsl使用bean/constructor投影获取列子集

Question

@Entity
public class UserDemo implements Serializable {

    @Id
    private Long id;

    private String username;

    private String createdBy;
    @Version
    private int version;

    /***
     *
     * Getters and setters
     */
}

Page<UserDemo> findAll(Predicate predicate, Pageable pageable);

Answer 1

看来，在spring Data中有类似的东西之前，自定义存储库实现是目前应该走的路。

我查阅了http://static.springsource.org/spring-data/data-jpa/docs/current/reference/html/repositories.html#repositories.custom-implementations

下面是我的实现，它可以工作。但是，最好能在Spring-Data-JPA中直接使用此方法

public interface CustomQueryDslJpaRepository <T, ID extends Serializable>
        extends JpaRepository<T, ID>, QueryDslPredicateExecutor<T> {
    /**
     * Returns a {@link org.springframework.data.domain.Page} of entities matching the given {@link com.mysema.query.types.Predicate}.
     * This also uses provided projections ( can be JavaBean or constructor or anything supported by QueryDSL
     * @param constructorExpression this constructor expression will be used for transforming query results
     * @param predicate
     * @param pageable
     * @return
     */
    Page<T> findAll(FactoryExpression<T> factoryExpression, Predicate predicate, Pageable pageable);
}

第二步：中间接口实现

public class CustomQueryDslJpaRepositoryImpl<T, ID extends Serializable> extends QueryDslJpaRepository<T, ID>
        implements CustomQueryDslJpaRepository<T, ID> {

    //All instance variables are available in super, but they are private
    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 CustomQueryDslJpaRepositoryImpl(JpaEntityInformation<T, ID> entityInformation, EntityManager entityManager) {
        this(entityInformation, entityManager, DEFAULT_ENTITY_PATH_RESOLVER);
    }

    public CustomQueryDslJpaRepositoryImpl(JpaEntityInformation<T, ID> entityInformation, EntityManager entityManager,
                                 EntityPathResolver resolver) {

        super(entityInformation, entityManager);
        this.path = resolver.createPath(entityInformation.getJavaType());
        this.builder = new PathBuilder<T>(path.getType(), path.getMetadata());
        this.querydsl = new Querydsl(entityManager, builder);
    }

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

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

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

步骤3：创建一个自定义存储库工厂来替换默认的

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

    protected RepositoryFactorySupport createRepositoryFactory(EntityManager entityManager) {

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

        private EntityManager entityManager;

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

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

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

步骤4：使用自定义存储库工厂

@EnableJpaRepositories(repositoryFactoryBeanClass=CustomQueryDslJpaRepositoryFactoryBean.class)

<repositories base-package="com.acme.repository"  factory-class="com.acme.CustomQueryDslJpaRepositoryFactoryBean" />

public interface UserDemoRepository extends CustomQueryDslJpaRepository<UserDemo, Long>{
}

public class UserDemoService {
    @Inject 
    UserDemoRepository userDemoRepository;

    public Page<User> findAll(UserSearchCriteria userSearchCriteria, Pageable pageable) {
        QUserDemo user = QUserDemo.userDemo;
        return userDemoRepository.findAll(Projections.bean(UserDemo.class, user.id, user.username), UserPredicate.defaultUserSearch(userSearchCriteria), pageable);
    }

}