Laravel 5: camel-case to snake-case mapping for eloquent relations has been dropped - http://slashnode.com/definitive-laravel-4-to-laravel-5-migration-guide/

Article.php

<?php namespace App\Models;

class Article extends Model
{
    /** etc... */
    public function associatedUsers()
    {
        return $this->belongsToMany('...');
    }
    /** etc... */
}

$article = App\Models\Article::find(1);

// below: works in Laravel 4.2, but not Laravel 5
$article->associated_users;

// instead use this
$article->associatedUsers;