Composite ID in join-table

I have the following PostLike class:

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
public class PostLike extends BaseEntity {

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user;

    @ManyToOne
    @JoinColumn(name = "post_id")
    private Post post;
}

The class already has an ID field provided by parent BaseEntity class.

In the User class, I have the following field:

@OneToMany(mappedBy = "user", fetch = FetchType.LAZY)
Set<PostLike> userLikes = new HashSet<PostLike>();

And in the Post class:

@OneToMany(mappedBy = "post")
private Set<PostLike> postLikes = new HashSet<PostLike>();

I want a PostLike to have a composite primary key, which consists of user_id and post_id.
Thanks in advance.

As one way to do this you can use @EmbeddedId annotation and express this composite key with embeddable class:

@Entity
public class PostLike {

    @Embeddable
    private static class Id implements Serializable {
        
        @Column(name = "user_id")
        private Long userId;
        
        @Column(name = "post_id") 
        private Long postId;

        public Id() {
        }

        public Id(Long userId, Long postId) {
            this.userId = userId;
            this.postId = postId;
        }

        // equals and hashCode
    }

    @EmbeddedId
    Id id = new Id();

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user;

    @ManyToOne
    @JoinColumn(name = "post_id")
    private Post post;


    public PostLike() {
    }

    public PostLike(User user , Post post) {
        this.user = user;
        this.post = post;

        this.id.postId = post.getId();
        this.id.userId = user.getId();

        post.getUserLikes().add(this);
        user.getUserLikes().add(this);
    }
        ... // getters and setters
}

Some notes:
from javadoc of @EmbeddedId
> There must be only one <code>EmbeddedId</code> annotation and
no <code>Id</code> annotation when the <code>EmbeddedId</code> annotation is used.

from Java Persistence with Hibernate
> The primary advantage of this strategy is the possibility for bidirectional navigation.
...
> A disadvantage is the more complex code needed to manage the
intermediate entity instances to create and remove links, which you have to save
and delete independently.