Get inverse relationship with Laravel

Question

I am creating a forum system that is divided by sections. Each section contains categories, each category contains topics. Ex:

Administração _
               |_Regras da do fórum
               |_Sugestões e críticas

Aeromodelismo _
               |_Elétricos _
               |_Glow       |-Tópico 1
                            |-Tópico 2
                            |-Tópico N

When entering the forum I need to pick up the last topics answered where (Where) id of section = X.

In summary I need to get the last topics answered within a specific section, but one has to consider that in the table 'topics' the foreign key references the category, and in the table 'categories' the foreign key references the section, that is, the topics are 'grandchildren' of the sections.

Answer 1

Well, I would implement it that way:

It would unify categories and sessions into a single table by adding an "id_parent" column, referencing the table itself and allowing nulls. So the sessions would be the categories with id_pai null.

To return the topics of a specific session, just one DB::table('sessoes')->where('id_pai', 4)->get()->toArray(); to have an array with the id of all categories and finally use this array in a query with whereIn

Example:

$categorias = DB::table('sessoes')->where('id_pai', 4)->get()->toArray();
$topicos = DB::table('topicos ')
                    ->whereIn('id',$categorias)->get();

Answer 2

If the problem is just ordering...

Model::orderBy('id', 'DESC')->get();

More information http://laravel.com/docs/eloquent#query-Scopes