How to get the ids of many to many relation? - php

Question

I have two models, Foo and Bar:
​​​​​
class Foo extends Eloquent {
protected $table = 'foos';
protected $fillable = array('name');
public $timestamps = false;
public function bars() {
return $this->belongsToMany('bar','foos_bars');
}
}
class Bar extends Eloquent {
protected $table = 'bars';
protected $fillable = array('name');
public $timestamps = false;
public function foos() {
return $this->belongsToMany('foo','foos_bars');
}
}
I'm trying to get all the Foo models and their related bars like this and then output it in json:
class FooController extends \BaseController {
/**
* Display a listing of the resource.
*
* #return Response
*/
public function index()
{
$foos = Foo:with('bars')->get();
return Response::json(array(
'foos' => $foos->toArray()
),200);
}
}
The problem I'm having is with the output. This will output something like this:
{
"foos": [
{
"id": 1,
"name": "Foo 1",
"bars": [
{
"id": 1,
"name": "Bar 1",
"pivot": {
"foo_id": 1,
"bar_id": 1
}
},
{
"id": 2,
"name": "Bar 2",
"pivot": {
"foo_id": 1,
"bar_id": 2
}
},
{
"id": 3,
"name": "Bar 3",
"pivot": {
"foo_id": 1,
"bar_id": 3
}
}
]
}
]
}
But all I really want is:
{
"foos":
[{
"id": 1,
"name": "Foo 1",
"bars": [1, 2, 3]
}]
}
Right now, I've been iterating over $foos like this to get the right code:
foreach($foos as &$foo) {
$bar_ids = array();
foreach($foo->bars as $bar) {
$bar_ids[] = $bar->pivot->bar_id;
}
unset($foo->bars);
$foo->bars = $bar_ids;
}
But this seems to complicated and adds a lot of complexity I'm trying to get rid of. Is there a simpler way to get the desired output?
Thanks for any assistance.

Answer 1

Use transformers/presenters for such thing, fractal is one you could consider. However, you can do pretty much the same easily with Eloquent:
// Foo
protected $hidden = ['bars']; // don't show the collection in json
protected $appends = ['barsIds']; // but show additional info you need via accessor
public function getBarsIdsAttribute()
{
return $this->bars->lists('id');
}
Now you can use the accessor directly:
$foo->barsIds; // [1,5,10]
and it is automaticly appended to the toArray/toJson output:
{
"foos": [
{
"id": 1,
"name": "Foo 1",
"barsIds": [1,5,10]
}
]
}
IMPORTANT When you want to output collection of foos, then remember to eager load bars relation, otherwise you will experience N+1 query issue.

Answer 2

You can use the lists method.
$foo->bars->lists('id');
Will give you an array of foo's bar ids.
Available on:
Illuminate\Database\Eloquent\Builder::lists
Illuminate\Database\Query\Builder::lists
Illuminate\Support\Collection::lists
some additional advice:
To return the data in the format you want, it might be nice to use transformers, like from the fractal package (or make a simpler version on your own, depending on your requirements).
The idea is to have something in the middle to format your data instead of dumping your models to a response in your controllers. It could directly take care of your issue and have added benefits like casting properties to types (like boolean and integers) as well as insulating your controllers from database changes.
A transformer could look something like this:
class FooTransformer extends TransformerAbstract
{
/**
* Transform this item object into a generic array.
*
* #param Foo $foo
* #return array
*/
public function transform(Foo $foo)
{
return [
'id' => (int) $foo->id,
'name' => $foo->name,
'bars' => $foo->bars->lists('id'),
];
}
}

Answer 3

It sounds like you want a GROUP CONCAT in the foo query, for which you'd need to use DB::raw().
There's also the lists() method, e.g.
public function barsIds() {
return $this->belongsToMany('bar','foos_bars')
->lists('id');
}