注意 @org.hibernate.annotations.Formula 使用 native SQL 因此可能导致依赖具体的 DB 从而影响 database portability 。

@Formula mapping usage

package org.example.demo.hibernate;

import javax.persistence.Entity;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Persistence;

import org.hibernate.annotations.Formula;

public class Test {
    public static void main(String[] args) {
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("test");
        EntityManager em = factory.createEntityManager();

        em.getTransaction().begin();
        Account account = new Account();
        account.credit = 5000d;
        account.rate = 1.25 / 100;
        em.persist(account);
        em.getTransaction().commit();

        em.clear();

        Account a = em.find(Account.class, account.id);
        // 62.5
        System.out.println(a.interest);

        em.close();
        factory.close();
    }

    @Entity(name = "Account")
    public static class Account {
        @Id
        @GeneratedValue
        Long id;
        Double credit;
        Double rate;
        @Formula(value = "credit * rate")
        Double interest;
    }
}

生成 SQL

drop table if exists Account cascade
drop sequence if exists hibernate_sequence

create sequence hibernate_sequence start 1 increment 1
create table Account (id int8 not null, credit float8, rate float8, primary key (id))
select nextval ('hibernate_sequence')
insert into Account (credit, rate, id) values (5000.0, 0.0125, 1)

select test_accou0_.id as id1_0_0_, test_accou0_.credit as credit2_0_0_, test_accou0_.rate as rate3_0_0_, test_accou0_.credit * test_accou0_.rate as formula0_0_ from Account test_accou0_ where test_accou0_.id=1

@Formula 可以包含子查询