休眠：多对多删除删除整个表

Question

我通过实体AppointmentRequest 在Doctor 和Patient 之间建立了多对多关系。但是，当我删除 1 个 Doctor 时，每个通过 AppointmentRequest 表关联的 Doctor 和 Patient 都会被删除。

这是我的代码：

医生

public class Doctor implements Person {

    private List<AppointmentRequest> appointmentRequests = new ArrayList<AppointmentRequest>();

    @OneToMany(mappedBy="doctor", targetEntity = AppointmentRequest.class, 
             fetch=FetchType.EAGER, cascade= CascadeType.ALL) 
    public List<AppointmentRequest> getAppointmentRequests() {
        return this.appointmentRequests;
    }

}

患者

public class Patient implements Person {

   private List<AppointmentRequest> appointmentRequests = new ArrayList<AppointmentRequest>();

   @OneToMany(mappedBy="patient", targetEntity = AppointmentRequest.class, 
         fetch=FetchType.EAGER, cascade= CascadeType.ALL) 
   public List<AppointmentRequest> getAppointmentRequests() {
       return this.appointmentRequests;
   }

}

约会请求

public class AppointmentRequest {

   private Doctor doctor;
   private Patient patient;

   @ManyToOne (fetch = FetchType.EAGER, cascade= CascadeType.ALL) 
   @JoinColumn(name="doctor_id") 
   public Doctor getDoctor() {
       return doctor;
   }

   @ManyToOne (fetch = FetchType.EAGER, cascade= CascadeType.ALL) 
   @JoinColumn(name="patient_id") 
   public Patient getPatient() {
       return patient;
   }
}

医生删除代码

public void deleteDoctor(String doctor_name) {
    Session session = sessionFactory.openSession();
    Doctor doctor = new Doctor();
    try {
        session.beginTransaction();
        Query query = session.getNamedQuery("Doctor.findByName");
        query.setString("name", doctor_name);
        doctor = (Doctor) query.uniqueResult();
        if(doctor == null) {
            throw new NullPointerException();
        }
        List<AppointmentRequest> appointments = doctor.getAppointmentRequests();
        for(AppointmentRequest appointment:appointments) {
            appointment.setDoctor(null);
        }
        session.delete(doctor);
        session.getTransaction().commit();
    }
    finally {
        session.close();
    }
}

Answer 1

在ManyToMany 与连接表的关系中，连接表的存在只是为了创建关系。当关系被破坏/删除时休眠 将自动更新/删除与表中该关系对应的行条目。连接表没有等效的实体定义。换句话说 连接表中的行本身并不代表实体。它没有身份，不能被其他实体共享/引用。但是，在您的情况下，您建模的方式是 您已经创建了一个单独的实体AppointmentRequest，它是可共享/可引用的并封装了关系。这种设计通常是在除了两个相关实体之外，您还有一些其他属性要存储时完成，例如创建日期、创建者等。然后您可以要求实体说明此关系是何时创建的或由谁创建的。所以你需要问的问题是你是否只想要一个many-to-many 关系或者你的关系本身就是一个实体。