Updating multiple tables when saving entity Spring MVC Angular - angularjs

Question

I have a problem with saving entity with references to database using
Spring MVC and AngularJS.
My entities:
Entity
#Table(name = "comment")
public class Comment {
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
#Column(name = "id", nullable = false)
private Long id;
#Column(name = "creation_date", nullable = false)
private Date creationDate;
#Column(name = "comment", nullable = false)
private String comment;
#ManyToOne
#JoinColumn(name = "article", nullable = false)
private Article article;
#ManyToOne
#JoinColumn(name = "user", nullable = false)
private User user;
}
#Entity
#Table(name = "article")
public class Article {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id", nullable = false)
private Long id;
#ManyToOne
#JoinColumn(name="user", nullable=false)
private User user;
...
}
How can I save new Article but at the same time add new entity to Comment table?
How can two updates be performed in one transaction?
How sholud I connect request from angular with controller, and how sholud they look?
Angular:
$http({
url : ..../new,
method : POST,
data : ?
})
#RestController
#RequestMapping(value = "/new", method = RequestMethod.POST)
public Article addArticle(#RequestBody Article article, ?) {
article.setId(null);
return articleService.save(article);
//but how to save comment?
}
Thank You!