Jpa标准API计数

Question

@PersistenceContext
    public EntityManager em;

......

public Page<UserDTO> findByCriteria(String filters, Pageable pageable) {
        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<UserDTO> cq = cb.createQuery(UserDTO.class);
        Root<UserDTO> iRoot = cq.from(UserDTO.class);
        List<Predicate> predicates = new ArrayList<Predicate>();

        if (StringUtils.isNotEmpty(filters)) {
            predicates.add(cb.like(cb.lower(iRoot.<String>get("login")), "%" + filters.toLowerCase() + "%"));
        }

        Predicate[] predArray = new Predicate[predicates.size()];
        predicates.toArray(predArray);

        CriteriaQuery<Long> sc = cb.createQuery(Long.class);
        sc.select(cb.count(iRoot));

        sc.where(predArray);
        Long count = em.createQuery(sc).getSingleResult();

        cq.where(predArray);

        List<Order> orders = new ArrayList<Order>(2);
        orders.add(cb.asc(iRoot.get("name")));
        orders.add(cb.asc(iRoot.get("desc")));

        cq.orderBy(orders);
        TypedQuery<UserDTO> query = em.createQuery(cq);

        Page<UserDTO> result = new PageImpl<UserDTO>(query.getResultList(), pageable, count);


        return result;
    }

public Page<UserDTO> findByCriteria(String columnName, String filters, Pageable pageable) {
        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<UserDTO> cq = cb.createQuery(UserDTO.class);
        Root<UserDTO> iRoot = cq.from(UserDTO.class);
        List<Predicate> predicates = new ArrayList<Predicate>();

        if (StringUtils.isNotEmpty(filters)) {
            predicates.add(cb.like(cb.lower(iRoot.<String>get(columnName)), "%" + filters.toLowerCase() + "%"));
        }

        Predicate[] predArray = new Predicate[predicates.size()];
        predicates.toArray(predArray);

        Long count = calculateCount(filters);

        cq.where(predArray);

        List<Order> orders = new ArrayList<Order>(2);
        orders.add(cb.asc(iRoot.get("firstName")));
        orders.add(cb.asc(iRoot.get("lastName")));

        cq.orderBy(orders);
        TypedQuery<UserDTO> query = em.createQuery(cq);

        Page<UserDTO> result = new PageImpl<UserDTO>(query.getResultList(), pageable, count);


        return result;
    }

    public Long calculateCount(String filters) {
        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<Long> sc = cb.createQuery(Long.class);
        Root<UserDTO> iRoot = sc.from(UserDTO.class);
        List<Predicate> predicates = new ArrayList<Predicate>();

        if (StringUtils.isNotEmpty(filters)) {
            predicates.add(cb.like(cb.lower(iRoot.<String>get("login")), "%" + filters.toLowerCase() + "%"));
        }

        Predicate[] predArray = new Predicate[predicates.size()];
        predicates.toArray(predArray);

        sc.select(cb.count(iRoot));

        sc.where(predArray);
        Long count = em.createQuery(sc).getSingleResult();

        return count;

    }

Answer 1

正如注释中所预期的，您需要显式添加CriteriaQuery#from()方法：

sc.from(UserDTO.class);

通常不使用from方法，因为API提供程序默认为CriteriaQuery构造函数中指定的实体类。但是在本例中不是，因为类是长并且它不对应于实体类。

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