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@Data
@NoArgsConstructor
@Entity
public class Applicant {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @OneToOne
    @JoinColumn(name = "cv_id", referencedColumnName = "id")
    private Cv cv;
    
    public Applicant(Cv cv) {
        this.cv = cv;
    }
}

@Data
@NoArgsConstructor
@Entity
public class Education {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @ManyToOne
    @JoinColumn(name = "cv_id", referencedColumnName = "id")
    private Cv cv;
    
    public Education(Cv cv) {
        this.cv = cv;
    }
}

@Data
@NoArgsConstructor
@Entity
public class Cv {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @OneToOne(mappedBy = "cv", cascade = CascadeType.ALL)
    private Applicant applicant;

    @OneToMany(mappedBy = "cv", cascade = CascadeType.ALL)
    private Set<Education> educations = new HashSet<>();

    @OneToMany(mappedBy = "cv", cascade = CascadeType.ALL)
    private Set<Experience> experiences = new HashSet<>();
    
    public Cv(Applicant applicant, Set<Education> educations, Set<Experience> experiences) {
        this.applicant = applicant;
        this.educations = educations;
        this.experiences = experiences;
    }

}


public Cv save(Cv cv) {
    return cvRepository.save(cv);
}
// Hibernate: insert into cv (id) values (default)
// Hibernate: insert into applicant (cv_id,id) values (?,default)
// Hibernate: insert into education (cv_id,id) values (?,default)