Many to one relation with inherited objects - Postgres - spring

Question

I'm building an application in which I need a single login page. However, there are two 'sorts' of users: Clients and Trainers. My domain looks like this:
User
|
+-----+-----+
| |
Person Trainer
My user will contain email, password etc. so I can use this table to verify my login requests.
A Trainer should store a list of persons, and a person should have 1 trainer.
The one to many side works, the trainer can store a list of Person class objects, but I can't link back to a trainer via a client.
This is my User class:
package com.example.demo.model;
import javax.persistence.*;
#Entity
#Inheritance
#Table(name="users")
public abstract class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String email;
public User(){}
public User(String email) {
this.email = email;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
}
The Person class:
package com.example.demo.model;
import javax.persistence.*;
#Entity
public class Person extends User {
#Column
private int age;
#ManyToOne
#JoinColumn
private Trainer trainer;
public Person(){}
public Person(String email, int age) {
super(email);
this.age = age;
}
}
The Trainer class:
package com.example.demo.model;
import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;
#Entity
public class Trainer extends User {
#Column
private String description;
#OneToMany(mappedBy = "trainer", fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true)
private List<Person> clients;
public Trainer(){}
public Trainer(String email, String description) {
super(email);
this.description = description;
}
public void addClient(Person person){
this.clients = new ArrayList<>();
this.clients.add(person);
}
}
How should I access a client's trainer via the ManyToOne annotation? Or are there other options?
Thanks in advance!

Answer 1

Dont initialize list in addClient(). You are overwriting/deleting existing clients. Do it in field declaration.
#OneToMany(...)
private List<Person> clients = new ArrayList<>();
Set both sides of relation:
public void addClient(Person person){
person.setTrainer(this);
this.clients.add(person);
}