最近项目上用就hibernate+spring data jpa，一开始感觉还不错，但是随着对业务的复杂，要求处理一些复杂的sql，就顺便研究了下，把结果记录下，以便日后查看。用到Specification，需要继承JpaSpecificationExecutor接口。（下面代码有的分页从0开始作为第一页，有的从1开始作为作为第一页，我也忘记，请自己测试）
DAO层：
import java.util.List;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;
@Repository
public interface CameraInfoRepo extends JpaRepository<CameraInfoPO, String>, JpaSpecificationExecutor<CameraInfoPO> {
@Query("select c from CameraInfoPO c where c.deviceInfo.id = ?1")
public List<CameraInfoPO> findCamerasByDeviceId(String listDeviceInfoId);
//更新之后不清空缓存，在一个事务里查询到旧数据(hibernate)
@Modifying
@Query(value = "update CameraInfoPO c set c.isEnabled = 1 where c.id = ?1")
public void updateEnabled(String cameraId);
//更新之后清空缓存，不保留旧对象(hibernate)
@Modifying(clearAutomatically = true)
@Query(value = "update CameraInfoPO c set c.isEnabled = 0 where c.id = ?1")
public void updateUnEnabled(String cameraId);
//带条件的分页查询
public Page<CameraInfoPO> findByIsEnabled(Integer isEnabled, Pageable pageable);
}
DAO实现层
import java.util.ArrayList;
import java.util.List;
import javax.annotation.Resource;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.TypedQuery;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageImpl;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.domain.Specification;
import org.springframework.stereotype.Repository;
@Repository
public class CameraInfoRepoImpl {
@PersistenceContext
private EntityManager em;
@Resource
private CameraInfoRepo cameraInfoRepo;
public Page<CameraInfoPO> findCameraInfoByPage(Pageable pageable, Integer isEnabled) {
//CriteriaBuilder,用来构建CritiaQuery的构建器对象
CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
//CriteriaQuery,它包含着查询语句的条件各个部分，比如：select 、from、where、group by、order by等
CriteriaQuery<CameraInfoPO> criteriaQuery = criteriaBuilder.createQuery(CameraInfoPO.class);
//查询根，用于获取查询实例的属性，通过CriteriaQuery的from方法获取
Root<CameraInfoPO> rootFrom = criteriaQuery.from(CameraInfoPO.class);
//查询条件
List<Predicate> predicates = new ArrayList<Predicate>();
if (null != isEnabled) {
Predicate predicate = criteriaBuilder.equal(rootFrom.get("isEnabled").as(Integer.class), isEnabled);
predicates.add(predicate);
}
//格式化参数
criteriaQuery.where(criteriaBuilder.and(predicates.toArray(new Predicate[predicates.size()])));
//默认按照id排序（从小到大）
criteriaQuery.orderBy(criteriaBuilder.asc(rootFrom.get("id")));
//SQL查询对象
TypedQuery<CameraInfoPO> createQuery = em.createQuery(criteriaQuery);
//分页参数
Integer pageSize = pageable.getPageSize();
Integer pageNo = pageable.getPageNumber();
//计数查询结果条数
TypedQuery<CameraInfoPO> createCountQuery = em.createQuery(criteriaQuery);
// 实际查询返回分页对象
int startIndex = pageSize * pageNo;
createQuery.setFirstResult(startIndex);
createQuery.setMaxResults(pageable.getPageSize());
Page<CameraInfoPO> pageRst =
new PageImpl<CameraInfoPO>(createQuery.getResultList(), pageable, createCountQuery.getResultList().size());
return pageRst;
}
//制造查询条件结果(建议存放map)
private Specification<CameraInfoPO> getWhereClause(final Integer isEnabled) {
return new Specification<CameraInfoPO>() {
public Predicate toPredicate(Root<CameraInfoPO> r, CriteriaQuery<?> q, CriteriaBuilder cb) {
Predicate predicate = cb.conjunction();
if (null != isEnabled) {
predicate = cb.equal(r.get("isEnabled").as(Integer.class), isEnabled);
}
return predicate;
}
};
}
//单表根据查询条件的分页
public Page<CameraInfoPO> findCameraInfoByPageForJpa(Pageable pageable, Integer isEnabled) {
Specification<CameraInfoPO> spec = getWhereClause(isEnabled);
Page<CameraInfoPO> pageRst = cameraInfoRepo.findAll(spec, pageable);
return pageRst;
}
}
还有另外一种就更简单了，如果只是根据表里面的一个或者几个字段，可以直接写jpa实现，不用复杂
Pageable pageable = new PageRequest(1, 1); Page<CameraInfoPO> page = cameraInfoRepo.findByIsEnabled(1, pageable);
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。
