[Java] [JPA] Map @OneToMany, @manytoone example

Employee.java

import javax.persistence.*;
import java.util.HashMap;
import java.util.Map;

@Entity
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public int id;
    public String firstName;
    public String lastName;

    @OneToMany(mappedBy = "owner", cascade = CascadeType.ALL)
    @MapKeyColumn(name = "phone_type")
    public Map<String, Phone> phones = new HashMap<>();

    @Override
    public String toString() {
        return String.format("Employee #%d : %s %s", id, firstName, lastName);
    }
}

ER diagram.png

Phone.java

import javax.persistence.*;

@Entity
public class Phone {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public int id;
    public String number;
    public String provider;

    @ManyToOne
    public Employee owner;

    @Override
    public String toString() {
        return String.format("Phone #%d : %s (%s)", id, number, provider);
    }
}

• ver 01: uni-directional @OneToMany phone.onwer
• ver 02: @ManyToOne employee.phones
• ver 03: ver 01 + ver 02
• ver 04: refine relationship : bi-directional employee ↔ phone
• ver 05: customize the map-key column