The error doesn't come from the code you showed, it's probably in the view and the reason for that is that I believe you try to do something like this:

$category->types->tipo();

That being said, you try to call Types method on the Collection of Types models not on a single model.

OK. I hope to explain better.

I have two tables

mysql> select * from eventi_tipo;

+----+-----------+--------------+
| id | Type     | category_id |
+----+-----------+--------------+
|  2 | Opera     |            1 |      
|  3 | Film       |            2  |      
|  4 | Balletto   |            1  |
|  6 | Horror     |            2 |
+----+-----------+--------------+
4 rows in set (0.00 sec)

mysql> select * from categories;

 +----+-----------+
 | id | category | 
+----+-----------+
 |  1 |  Teatro     |
 |  2 | Film      |
+----+-----------+
2 rows in set (0.00 sec)

Now in my controller Types I have this

public function index()
{
	$types = Types::with('categories')->get();
	return View::make('eventi_tipo.index', $type);
}

And in my models:

<?php

class Category extends \Eloquent {

protected $fillable = [];

protected $table = 'categories';

public function types()
{
	return $this->hasMany('Types','category_id');
}
}

<?php class EventiTipo extends \Eloquent { protected $fillable = []; protected $table ='types'; public function categories() { return $this->belongsTo('Categories'); } } The problem is the in my result I have the ID of th categories and not their name (Teatro, Film)