Hibernate @Formula （公式） 使用教程

使用方法

private Long usersSize;

       @Formula("(id * 8888888)")
	@JsonProperty
	public Long getUsersSize(){
		return usersSize;
	}
	
	
	public void setUsersSize(Long usersSize) {
		this.usersSize = usersSize;
	}
略。。。。

注意 必须使用（）来包裹sql片段，hibernate不会在数据库创建userSize对应的列

查看下生成的hibernate 生成的 sql，很明显是在数据库做了运算

select agent0_.id as id1_, agent0_.acl_code as acl2_1_, agent0_.acl_type as acl3_1_, agent0_.created_by 
as created4_1_, agent0_.created_dt as created5_1_, agent0_.updated_by as updated6_1_, agent0_.updated_dt 
as updated7_1_, agent0_.version as version1_, agent0_.agent_addres as agent9_1_, agent0_.agent_city 
as agent10_1_, agent0_.agent_county as agent11_1_, agent0_.agent_name as agent12_1_, agent0_.agent_province 
as agent13_1_, agent0_.agent_scale as agent14_1_, agent0_.zip_code as zip15_1_, agent0_.biz_lic_reg_no 
as biz16_1_, agent0_.join_date as join17_1_, agent0_.oper_org_type as oper18_1_, agent0_.org_code_cert_no 
as org19_1_, (agent0_.id * 8888888) as formula0_ from agent_agent agent0_ order by agent0_.created_dt 
desc limit 15

甚至你可以这样玩：

查询该代理下用户总数

@Formula("(select count(*) from tbl_auth_user o where o.agent_id = id)")

id 代表当前表的id

@Formula("(select count(*) from tbl_auth_user o where o.agent_id = id)")
	@JsonProperty
	public Long getUsersSize(){
		return usersSize;
	}

hibernate生成的 sql

select agent0_.id as id1_, agent0_.acl_code as acl2_1_, agent0_.acl_type as acl3_1_, agent0_.created_by 
as created4_1_, agent0_.created_dt as created5_1_, agent0_.updated_by as updated6_1_, agent0_.updated_dt 
as updated7_1_, agent0_.version as version1_, agent0_.agent_addres as agent9_1_, agent0_.agent_city 
as agent10_1_, agent0_.agent_county as agent11_1_, agent0_.agent_name as agent12_1_, agent0_.agent_province 
as agent13_1_, agent0_.agent_scale as agent14_1_, agent0_.zip_code as zip15_1_, agent0_.biz_lic_reg_no 
as biz16_1_, agent0_.join_date as join17_1_, agent0_.oper_org_type as oper18_1_, agent0_.org_code_cert_no 
as org19_1_, (select count(*) from tbl_auth_user o where o.agent_id = agent0_.id) as formula0_ 
from agent_agent agent0_ order by agent0_.created_dt desc limit 15

更多用例

@Formula("(select min(o.creation_date) from Orders o where o.customer_id = id)")
private Date firstOrderDate;

@Formula("(select max(o.creation_date) from Orders o where o.customer_id = id)")
private Date lastOrderDate;

@Formula("(select coalesce(extract ('day' from age(max(o.creation_date))), 9999) from Orders o where o.customer_id = id)")
private int daysSinceLastOrder;

 @Formula （公式）虽好，但是不要滥用哦