JPA: how can i map a property to a derived column that is based on a COUNT from other tables (Without incurring in n+1 select problems?)

These are the entities defined in my project:

Post

@Entity
public class Post implements Serializable {
    public enum Type {TEXT, IMG}

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    protected Integer id;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "section_id")
    protected Section section;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "author_id")
    protected User author;

    @Column(length = 255, nullable = false)
    protected String title;

    @Column(columnDefinition = "TEXT", nullable = false)
    protected String content;

    @Enumerated(EnumType.STRING)
    @Column(nullable = false)
    protected Type type;

    @CreationTimestamp
    @Column(nullable = false, updatable = false, insertable = false)
    protected Instant creationDate;

    @Column(insertable = false, updatable = false)
    protected Integer votes;  
    
    /*accessor methods*/
}

Comment

@Entity
public class Comment implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    protected Integer id;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "post_id")
    protected Post post;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "author_id")
    protected User author;

    @ManyToOne(fetch = FetchType.LAZY, optional = true)
    @JoinColumn(name = "parent_comment_id")
    protected Comment parentComment;

    @Column(columnDefinition = "TEXT", nullable = false)
    protected String content;

    @CreationTimestamp
    @Column(nullable = false, updatable = false, insertable = false)
    protected Instant creationDate;

    @Column(insertable = false, updatable = false)
    protected Integer votes;

    @Column(insertable = false, updatable = false)
    protected String path;
    
    /*accessor methods*/
}  

As you can see, aggregations are only tracked from the child's point of view: there are no @ManyToOne relationships due to a design choice.

However, I'd like to add a commentCount field to the Post entity. This field should be loaded eagerly (since it is always read in my use cases and a COUNT statement isn't that costly... i guess)

These are the options I'm currently aware of:

• Use the @Formula or the @PostLoad annotations: there would be N+1select statements

• Retrieve the posts, then call another repository method that uses the IN operator with all the retrieved posts as argument:

    select post, count(comment) from Post post, Comment comment where comment.post in (:posts) group by comment.post
  

  (Given that my data access layer might load even 50 posts at once, would a 50 parameters long in be optimal?)

• Create a non-mapped entity attribute, then take care of filling it manually in all repository methods involving Post with a join: i'd like to avoid this.

• Store commentCount in the database and mantain it with triggers: could be an option, but it's not the focus of this question (I'm not allowed to touch the schema)

What can be a valid solution? I'm using Hibernate but i prefer implementation-agnostic solutions (Implementation-specific options won't be ignored, though)