Question

In Play framework how do I list only a certain number of object from database instead of all.
Suppose that I have this Post class that has a @OneToMany relation with Comments just like this

public class Post extends Model {   
@ManyToOne
    public User user;
    public String name;
    public String description;
    public String image;
    public Date created_date;

    @OneToMany(mappedBy="post", cascade=CascadeType.ALL)
    public List<Comment> comments;
    ....
}

How do I only list top 5 comments for each post at the template? I’ve done this, but it shows all comments

#{list items:post.comments, as:'comment'}
    <p>${comment.comment}</p>
#{/list}    

Thanks

Answer 1

You can just use standard Java to get the sub list

#{list items:post.comments.subList(0,5), as:'comment'}
    <p>${comment.comment}</p>
#{/list}    

The above will return an array index out of bounds if there are less than 5 comments though, so you can either put some more logic in the template (as below), or you could create a getter method in your Post model that gets the top5 comments, and just call this instead (which is probably the cleaner and preferred option.

The extra logic in the template would look like

#{list items:post.comments.subList(0, Math.min(5, post.comments.size())), as:'comment'}
    <p>${comment.comment}</p>
#{/list}    

If you agree that this is too much logic in your view, and want to encapsulate it in your Model, you could do the following.
The extra logic in your view may look like

public List<Comment> getTop5() {
    return comments.subList(0, Math.min(5, comments.size());
}

And then your controller would be

#{list items:post.top5, as:'comment'}
    <p>${comment.comment}</p>
#{/list}