JPA/hibernate @joincolumns 联合主键关联
https://blog.csdn.net/paristao/article/details/20534399
这里我有2个entity，用过id1 + id2 映射
首先JPA 要求联合主键必须注册一个PK 类,自己override hashcode/equal方法
Class ProjectId {
    int departmentId;
    long projectId;
}

@Entity @IdClass(ProjectId.class)
public class Project {
    @Id int departmentId;
    @Id long projectId;
     :
}

然后在引用类中用joincolums关联
@JoinColumns ({
		@JoinColumn(name="id1",referencedColumnName = "id1",insertable = false, updatable = false),
		@JoinColumn(name="id2",referencedColumnName = "id2",insertable = false, updatable = false)
	})
	private Hits hits;
开始的时候没有声明，一直遇到错误。后来发现documentation跟interface都声明了default = true。

所以如果只是关联嵌入某张table，应该声明成false

--Hibernate中@Embedded和@Embeddable注解的使用
https://blog.csdn.net/lmy86263/article/details/52108130

多条件聚合查询
https://blog.csdn.net/mengyinjun217/article/details/78356027?utm_source=blogxgwz6
    @PersistenceContext
    private EntityManager em;
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder(); 
		CriteriaQuery<Integer> query = criteriaBuilder.createQuery(Integer.class); 
		Root<BossOrder> root = query.from(BossOrder.class); 
		List<Predicate> predicates = new ArrayList<Predicate>();
		query.select(criteriaBuilder.sum(root.get("orderAmount"))); 
		Path<String> $delFlag = root.get("delFlag");
		Predicate _delFlag = criteriaBuilder.equal($delFlag, CommonConstants.DEL_FLAG_FALSE);
		if(findOrderTableRequest.getOrderStatus() != null){
			Path<String> $orderStatus = root.get("orderStatus");
			Predicate _orderStatus = criteriaBuilder.equal($orderStatus, findOrderTableRequest.getOrderStatus());
			predicates.add(_orderStatus);
		}else{
			Path<String> $orderStatus = root.get("orderStatus");
			Predicate _orderStatus = criteriaBuilder.notEqual($orderStatus, OrderStatus.UNPAID);
			predicates.add(_orderStatus);
		}
	    Predicate[] p = new Predicate[predicates.size()];
	    query.where(criteriaBuilder.and(_delFlag,criteriaBuilder.and(predicates.toArray(p))));
		Integer singleResult = entityManager.createQuery(query).getSingleResult();

List<Object[]> sumAmountList = bossExpertAmountDao.sumAmount();
    	Object[] sumAmount = sumAmountList.get(0);
        apiReturn.setTotalIncome(((BigDecimal)sumAmount[0]));
        apiReturn.setTotalBalance(((BigDecimal)sumAmount[1]));
        apiReturn.setTotalTransferBalance(((BigDecimal)sumAmount[2]));
        apiReturn.setTotalFreezingAmount(((BigDecimal)sumAmount[3]));
        apiReturn.setCode(CommonConstants.ReturnCode.SUCCESS);
@Query(value = "SELECT SUM(income),SUM(balance),SUM(transfer_balance),SUM(freezing_amount) " +
			"FROM boss_expert_amount " +
			"WHERE del_flag = '0'",nativeQuery = true)
	List<Object[]> sumAmount();