Laravel: Unable to join tables

I am trying to join two tabels using Laravel (just started using it). One table holds user information, and the other table holds a users friend IDs.

So one user can have multiple friends. I have done this is the user class:

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
    protected $table="user_info";

    public function getFriends()
    {
        //user_id is the column in the user_friends table that should be linked to the id table in this class table (user_info)

        return $this->hasMany('App\UserFriends','user_id','id');
    }
}

And the other class (UserFriends)

namespace App;

use Illuminate\Database\Eloquent\Model;

class UserFriends extends Model
{
    protected $table="user_friends";
}

Then in a controller I call

$t = $this->sql_obj->getFriends()->toSql();

However, if I print the result of this it returns this:

select * from `user_friends` where `user_friends`.`user_id` is null and `user_friends`.`user_id` is not null

Why is it not joining the tables?

Thanks for any help!

via Chebli Mohamed