spring-data-jpa 是對資料庫訪問的簡化的封裝，可以幫助我們更加方便的實現對資料庫的各種操作。Spring Data JPA 規範方法的名字，根據符合規範的名字來確定方法需要實現什麼樣的邏輯，無需要我們過多關注sql等。一般情況下，對於單表操作非常方便，而涉及到多條件或者多表聯查時相對複雜一些。這裡簡單記錄一下jpa多條件查詢的相關api。

       多條件分頁查詢：其中User為查詢條件物件

public Page<User> findByPage(final User user, int page, int pageSize) throws Exception {
		Sort sort = new Sort(Direction.DESC, "registerTime");
		PageRequest pageRequest =  new PageRequest(page, pageSize, sort);
		
		return userDao.findAll(new Specification<User>(){
			@Override
			public Predicate toPredicate(Root<User> root,
					CriteriaQuery<?> query, CriteriaBuilder builder) {
				List<Predicate> predicates = new ArrayList<Predicate>();
				if(null != user.getUserType()){
					predicates.add(builder.equal(root.get("userType"), user.getUserType()));
				}
				if(null != user.getStatus()){
					predicates.add(builder.equal(root.get("status"), user.getStatus()));
				}
				query.where(predicates.toArray(new Predicate[predicates.size()]));
				return null;
			}
		}, pageRequest);
	}
 

   多表聯查： Question, Grade, Subject

public Page<Question> questionList(final String keyword,final String knowledge,final String type,final String itemBankId,final String gradeId,final String subjectId,Pageable pageable) {
    Page<Question> question = questionDao.findAll(new Specification<Question>() {
        @Override
        public Predicate toPredicate(Root<Question> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
            Predicate predicate = cb.conjunction();
            List<Expression<Boolean>> expressions = predicate.getExpressions();
            if (StringUtils.isNotBlank(keyword)) {
                expressions.add(cb.like(root.<String>get("keyword"), "%"+keyword+"%"));         
            }
            if (StringUtils.isNotBlank(knowledge)) {
                expressions.add(cb.like(root.<String>get("knowledge"), "%"+knowledge +"%"));    
            }
            if (NumberUtils.isDigits(type)) {
                expressions.add(cb.equal(root.<String>get("type"), type));   
            }
            if(StringUtils.isNotBlank(itemBankId)) {
                expressions.add(cb.equal(root.<String>get("puuid"), itemBankId));        
            }
            if(NumberUtils.isDigits(gradeId)) {
                expressions.add(cb.equal(root.<Grade>get("grade").<Long>get("id"), NumberUtils.toLong(gradeId)));       
            }
            if(NumberUtils.isDigits(subjectId)) {
                expressions.add(cb.equal(root.<Subject>get("subject").<Long>get("id"), NumberUtils.toLong(subjectId)));   
            }
            expressions.add(cb.equal(root.<Long>get("deleteBy"), 0));
            return predicate;
        }
    },pageable);
    return question;
}
 

    另記錄一下利用遊標查詢記錄總數:

public int findPageByQuery(final String sql,
            final Object[] parameters) {
        //em ==> EntityManager
        Session session = (Session) em.getDelegate();
        Query query = session.createQuery(sql);
        if (parameters != null) {
            for (int i = 0; i < parameters.length; i++) {
                query.setParameter(i, parameters[i]);
            }
        }
        //獲取遊標
        ScrollableResults sr = query.scroll();
        sr.last();
        int totalCount = sr.getRowNumber();
        return totalCount + 1;
    }