小编给大家分享一下JPA怎么通过Specification实现复杂查询，希望大家阅读完这篇文章之后都有所收获，下面让我们一起去探讨吧！
JPA 通过Specification实现复杂查询
JPA中继承BaseRepo之后，可以使用最基本的增删改查，如果想实现复杂查询，则需要借助Specification来完成这个功能：
下面就简单介绍一下Specification的使用
public void findAll(ConstructPlanPageReqEntity constructPlanPageReqEntity) {Integer pageNum = page.getPageNum(); Integer pageSize = page.getPageSize(); String costType = constructPlanPageReqEntity.getCostType(); String name = constructPlanPageReqEntity.getName(); String planMoneyStart = constructPlanPageReqEntity.getPlanMoneyStart(); String planMoneyEnd = constructPlanPageReqEntity.getPlanMoneyEnd(); String singMoneyEnd = constructPlanPageReqEntity.getSingMoneyEnd(); String signMoneyStart = constructPlanPageReqEntity.getSignMoneyStart(); long projectId = Long.parseLong(constructPlanPageReqEntity.getProjectId()); String status = constructPlanPageReqEntity.getStatus(); //分页 pageNum=pageNum-1; Pageable pageable = PageRequest.of(pageNum, pageSize);//多条件匹配查询 Specification specification= new Specification<ContractPlanBean>() { @Override public Predicate toPredicate(Root<ContractPlanBean> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) { ArrayList<Predicate> list = new ArrayList<>(); Path<String> costType1 = root.get("costType"); Path<String> name1 = root.get("name"); Path<Long> projectId1 = root.get("projectId"); Path<Object> status1 = root.get("status"); if (projectId>0){ list.add(criteriaBuilder.equal(projectId1,projectId)); } if (StringUtil.isNotEmpty(status)){ list.add(criteriaBuilder.equal(status1,status)); } //条件查询 if (StringUtil.isNotEmpty(costType)){ list.add(criteriaBuilder.equal(costType1,costType)); } //模糊查询 if (StringUtil.isNotEmpty(name)){ list.add(criteriaBuilder.like(name1,"%"+name+"%")); } //范围查询 if (StringUtil.isNotEmpty(planMoneyStart)&&StringUtil.isNotEmpty(planMoneyEnd)){ try { list.add(criteriaBuilder.between(root.get("planMoney"),NumberUtil.strToDouble(planMoneyStart),NumberUtil.strToDouble(planMoneyEnd))); } catch (Exception e) { throw new ApiException("规划金额查询失败"); } } //排序 criteriaQuery.orderBy(criteriaBuilder.asc(root.get("name"))); Predicate[] array = new Predicate[list.size()]; return criteriaBuilder.and(list.toArray(array)); } };}以上代码实现了多条件查询，其中需要重写toPredicate方法，具体参数：
用root.get()获取bean中的数据库对应字段
用criteriaBuilder来组建条件查询语句
上图是criteriaBuilder各种sql符号的方法名，根据需求组建不同的sql语句
criteriaBuilder.and(list.toArray(array))这句是最后定义各个sql查询条件的关系，这里用的and
至此，复杂sql语句就拼接完成，本人对Specification的使用未进行深入研究，个人觉得相对filter Strem的复杂查询来说Specification更繁琐，因此更倾向于通过Strem的复杂查询，这回就不多说了，下次就介绍下如何使用Stream进行复杂查询
spring-data-jpa Specification拼接复杂查询
public Page<ServiceItem> findAll(Map<String, String[]> params, ServiceItemConsumeStatus serviceItemConsumeStatus,ServiceItemStatus serviceItemStatus, Pageable pageable) { return dao.findAll(spec(serviceItemConsumeStatus, serviceItemStatus, params), pageable); } private Specification<ServiceItem> spec(final ServiceItemConsumeStatus serviceItemConsumeStatus, final ServiceItemStatus serviceItemStatus, Map<String, String[]> params) { Collection<SearchFilter> filters = SearchFilter.parse(params).values(); final Specification<ServiceItem> fsp = SearchFilter.spec(filters, ServiceItem.class); Specification<ServiceItem> sp = new Specification<ServiceItem>() { public Predicate toPredicate(Root<ServiceItem> root, CriteriaQuery<?> query, CriteriaBuilder cb) { Predicate pred = fsp.toPredicate(root, query, cb); if (ServiceItemConsumeStatus.可消费.equals(serviceItemConsumeStatus)) { pred = cb.and(pred, cb.gt(root.get("countLeft").as(int.class), 0)); } else if (ServiceItemConsumeStatus.消费完毕.equals(serviceItemConsumeStatus)) { pred = cb.and(pred, cb.le(root.get("countLeft").as(int.class), 0)); } if (serviceItemStatus != null) { pred = cb.and(pred, cb.equal(root.get("status"), serviceItemStatus)); } return pred; } }; return sp; }看完了这篇文章，相信你对“JPA怎么通过Specification实现复杂查询”有了一定的了解，如果想了解更多相关知识，欢迎关注编程网行业资讯频道，感谢各位的阅读！
