Saving to relational table Laravel 4 - php

Question

Basically I have a groups table with id and name,
I have another table with users_groups with id, group_id and user_id
I'm try to save when a user is created to the users_groups table, but when I use this code it saves what it can in the groups table. Is there something I'm doing wrong?
Account controller (saving user to db and set group to id 1)
$user = User::create(array(
'firstName' => $firstName,
'lastName' => $lastName,
'dateOfBirth' => $dateOfBirth,
'gender' => $gender,
'email' => $email,
'username' => $username,
'password' => Hash::make($password),
'code' => $code,
'active' => 0
));
Group::create([
'user_id' => $user->id,
'group_id' => '1' //1 is not assigned
]);
Group Model
class Group extends Eloquent
{
protected $fillable = array('name');
// DEFINE RELATIONSHIPS --------------------------------------------------
// define a many to many relationship
// also call the linking table
public function users() {
return $this->belongsToMany('User', 'users_groups', 'group_id', 'user_id');
}
}
User Model
use Illuminate\Auth\UserTrait;
use Illuminate\Auth\UserInterface;
use Illuminate\Auth\Reminders\RemindableTrait;
use Illuminate\Auth\Reminders\RemindableInterface;
class User extends Eloquent implements UserInterface, RemindableInterface {
protected $fillable =array('email', 'username', 'password', 'password_temp', 'code', 'active', 'firstName','lastName','gender','dateOfBirth');
use UserTrait, RemindableTrait;
/**
* The database table used by the model.
*
* #var string
*/
protected $table = 'users';
/**
* The attributes excluded from the model's JSON form.
*
* #var array
*/
protected $hidden = array('password', 'remember_token');
// Each User BELONGS to many Groups
// Define our pivot table also
public function groups() {
return $this->belongsToMany('Group', 'users_groups', 'user_id', 'group_id');
}
}

Answer 1

All information about saving relations can be found here
You need attach()
$user = User::create(array(
'firstName' => $firstName,
// ...
));
$user->groups()->attach(1); // 1 being the group_id