@Entity
public class Task {
@Id
@GeneratedValue
private Integer id;

private String title;
private String text;
private boolean done;
}

@Entity
public class TodolistUser {
@Id
@GeneratedValue
private Integer id;

private String login;
private String password;

@Autowired
@ElementCollection
private List<Task> tasks;
}

@Service
public class TodolistUserService {
    @Autowired
    private TodolistUserRepository repository;
}