"Three way" many-to-many relationship using Eloquent - php

Question

I have a simple database setup: Users, Groups, Pages - each are many to many.
See diagram: http://i.imgur.com/oFVsniH.png
Now I have a variable user id ($id), and with this I want to get back a list of the pages the user has access to, distinctly, since it's many-to-many on all tables.
I've setup my main models like so:
class User extends Eloquent {
protected $table = 'ssms_users';
public function groups()
{
return $this->belongsToMany('Group', 'ssms_groups_users', 'user_id','group_id');
}
}
class Group extends Eloquent {
protected $table = 'ssms_groups';
public function users()
{
return $this->belongsToMany('User', 'ssms_groups_users', 'user_id','group_id');
}
public function pages()
{
return $this->belongsToMany('Page', 'ssms_groups_pages', 'group_id','page_id');
}
}
class Page extends Eloquent {
protected $table = 'ssms_pages';
public function groups()
{
return $this->belongsToMany('Group', 'ssms_groups_pages', 'group_id','page_id');
}
}
I can get the groups the user belongs to by simply doing:
User::with('groups')->first(); // just the first user for now
However I'm totally lost on how to get the pages the user has access to (distinctly) with one query?
I believe the SQL would be something like:
select DISTINCT GP.page_id
from GroupUser GU
join GroupPage GP on GU.group_id = GP.group_id
where GU.user_id = $id
Can anyone help?
Thanks

Answer 1

TL;DR:
The fetchAll method below, in the MyCollection class, does the work. Simply call fetchAll($user->groups, 'pages');
Ok, assuming you managed to load the data (which should be done by eager-loading it, as mentioned in the other answer), you should loop through the Groups the User has, then loop through its Pages and add it to a new collection. Since I've had this problem already, I figured it would be easier to simply extend Laravel's own Collection class and add a generic method to do that.
To keep it simple, simply create a app/libraries folder and add it to your composer.json, under autoload -> classmap, which will take care of loading the class for us. Then put your extended Collection class in the folder.
app/libraries/MyCollection.php
use Illuminate\Database\Eloquent\Collection as IlluminateCollection;
class MyCollection extends IlluminateCollection {
public function fetchAll($allProps, &$newCollection = null) {
$allProps = explode('.', $allProps);
$curProp = array_shift($allProps);
// If this is the initial call, $newCollection should most likely be
// null and we'll have to instantiate it here
if ($newCollection === null) {
$newCollection = new self();
}
if (count($allProps) === 0) {
// If this is the last property we want, then do gather it, checking
// for duplicates using the model's key
foreach ($this as $item) {
foreach ($item->$curProp as $prop) {
if (! $newCollection->contains($prop->getKey())) {
$newCollection->push($prop);
}
}
}
} else {
// If we do have nested properties to gather, then pass we do it
// recursively, passing the $newCollection object by reference
foreach ($this as $item) {
foreach ($item->$curProp as $prop) {
static::make($prop)->fetchAll(implode('.', $allProps), $newCollection);
}
}
}
return $newCollection;
}
}
But then, to make sure your models will be using this class, and not the original Illuminate\Database\Eloquent\Collection, you'll have to create a base model from which you'll extend all your models, and overwrite the newCollection method.
app/models/BaseModel.php
abstract class BaseModel extends Eloquent {
public function newCollection(array $models = array()) {
return new MyCollection($models);
}
}
Don't forget that your models should now extend BaseModel, instead of Eloquent. After all that is done, to get all your User's Pages, having only its ID, do:
$user = User::with(array('groups', 'groups.pages'))
->find($id);
$pages = $user->groups->fetchAll('pages');

Answer 2

Have you tried something like this before?
$pages = User::with(array('groups', 'groups.pages'))->get();
Eager loading might be the solution to your problem: eager loading