ManyToMany relationship removes all entities

Question

I have two entities, user and movies. They're manytomany bidirectional relationship. My problem is that when I delete a movie via my controller it also removes all related with that movie entities. My user and this user roles and the movie entity. What have I to do, to get rid just off movie entity from the table when delete it and keep the user with his roles instead of removing them all.

@Data
@ToString
@EqualsAndHashCode
@Entity
@Table(name = "movies")
public class Movie {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name = "title")
    private String title;
    @Column(name = "description")
    private String description;
    @Column(name = "release_date")
    @Temporal(TemporalType.DATE)
    private Date release_date;
    @Column(name = "country")
    private String country;
    @Column(name = "category")
    private String category;
    @ManyToMany(mappedBy = "movies")
    @ToString.Exclude
    @EqualsAndHashCode.Exclude
    private Set<User> users = new HashSet<>();

@Data
@ToString
@Entity
@Table(name = "users")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name = "username")
    private String username;
    @Column(name = "password")
    private String password;
    @Transient
    private String confirmPassword;
    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "users_roles", joinColumns = {@JoinColumn(name = "user_id", referencedColumnName = "id")},
            inverseJoinColumns = {@JoinColumn(name = "role_id", referencedColumnName = "id")})
    @ToString.Exclude
    @EqualsAndHashCode.Exclude
    private Set<Role> roles = new HashSet<>();

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "users_movies", joinColumns = {@JoinColumn(name = "user_id", referencedColumnName = "id")},
            inverseJoinColumns = {@JoinColumn(name = "movie_id", referencedColumnName = "id")})
    @ToString.Exclude
    @EqualsAndHashCode.Exclude
    private Set<Movie> movies = new HashSet<>();

Answer 1

Well, I had to guess what your Role entity looks like so include complete examples. You didn't specify whether you were using Spring-Data-Jpa or just Jpa so who knows. Edit: in your examples you have finally clarified that you are using spring-data-jpa, but the concepts are the same as here anyway.

@Data
@ToString
@Entity
@Table(name = "roles")
public class Role {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToMany(mappedBy="roles")
    @ToString.Exclude
    @EqualsAndHashCode.Exclude
    private Set<User> users = new HashSet<>();

}

and to use

tx.begin();

User u1 = new User();
Role r1 = new Role();
u1.setRoles(Collections.singleton(r1));
Movie m1 = new Movie();
m1.setDescription("movie 1");
Movie m2 = new Movie();
m2.setDescription("movie 2");
u1.setMovies(Stream.of(m1, m2).collect(Collectors.toSet()));
em.persist(u1);

tx.commit();

// now to query
em.clear();

tx.begin();
User u = em.createQuery("from User u left outer join fetch u.movies where u.id = 1", User.class).getSingleResult();
Movie m = u.getMovies().stream().filter(mv->mv.getDescription().equals("movie 1")).findFirst().get();
u.getMovies().remove(m);
em.remove(m);
tx.commit();

and this creates the log

create table users (id bigint generated by default as identity (start with 1), password varchar(255), username varchar(255), primary key (id))
create table users_movies (user_id bigint not null, movie_id bigint not null, primary key (user_id, movie_id))
create table users_roles (user_id bigint not null, role_id bigint not null, primary key (user_id, role_id))
alter table users_movies add constraint FKt4hasm7tvj0vor58ql33xptjy foreign key (movie_id) references movies
alter table users_movies add constraint FKhhj9vi206o88q0typfntk3fek foreign key (user_id) references users
alter table users_roles add constraint FKj6m8fwv7oqv74fcehir1a9ffy foreign key (role_id) references roles
alter table users_roles add constraint FK2o0jvgh89lemvvo17cbqvdxaa foreign key (user_id) references users
insert into users (id, password, username) values (default, ?, ?)
insert into movies (id, category, country, description, release_date, title) values (default, ?, ?, ?, ?, ?)
insert into movies (id, category, country, description, release_date, title) values (default, ?, ?, ?, ?, ?)
insert into roles (id) values (default)
insert into users_movies (user_id, movie_id) values (?, ?)
insert into users_movies (user_id, movie_id) values (?, ?)
insert into users_roles (user_id, role_id) values (?, ?)
select user0_.id as id1_2_0_, movie2_.id as id1_0_1_, user0_.password as password2_2_0_, user0_.username as username3_2_0_, movie2_.category as category2_0_1_, movie2_.country as country3_0_1_, movie2_.description as descript4_0_1_, movie2_.release_date as release_5_0_1_, movie2_.title as title6_0_1_, movies1_.user_id as user_id1_3_0__, movies1_.movie_id as movie_id2_3_0__ from users user0_ left outer join users_movies movies1_ on user0_.id=movies1_.user_id left outer join movies movie2_ on movies1_.movie_id=movie2_.id where user0_.id=1
delete from users_movies where user_id=? and movie_id=?
delete from movies where id=?

Answer 2

Problem solved, instead of using mappedBy I added a JoinTable annotation also to Movie entity and now it works as it should.

Answer 3

this is the expected behavior when you use CascadeType.ALL, which implicitly includes CascadeType.REMOVE - that removes all the related entities on removing the owning entity.

Since you are using CascadeType.ALL on both sides of the association, as a result you end up deleting records more than what you actually intended.

To avoid this:

• You need to remove the CascadeType.ALL or change it to something appropriate like MERGE / PERSIST
• Handle the deletion of entities on your own.
• Consider using batch delete option specifying the associated entity id.