Laravel对象关系在foreach循环中不起作用

I have a typical model relation. I have the model QR, which hasMany Rating, and a Model Rating, which belongsTo Qr.

Now I want to output the Ratings, which belong to a single qr model, through a foreach loop like this:

            <table>
                <tr>
                    <th>ID</th>
                    <th>UnitID</th>
                    <th># of Ratings</th>
                </tr>

                @foreach($qrs as $qr->ratings)

                <tr>
                    <td>{{$qr->id}}</td>
                    <td>{{$qr->unit_id}}</td>
                    <td>{{$qr->ratings->count()}}</td>
                </tr>

                @endforeach
            </table>

This is my Controller:

public function index()
{
    //
    $unit = Unit::all()->first();
    $qrs = Qr::all()->first();
    return View::make('index')
        ->with('unit', $unit)
        ->with('qrs', $qrs);
}

Here are my two Models

Rating.php:

    class Rating extends \Eloquent {
    protected $guarded = [];

    public function qr(){
        return $this->belongsTo('Qr');
    }
}

Qr.php:

    class Qr extends \Eloquent {
    protected $guarded = [];

    public function unit(){
        return $this->belongsTo('Unit');
    }

    public function ratings(){
        return $this->hasMany('Rating');
    }
}

I actually want to output the count of ratings, a Qr-Code has. I know it is possible to do it somehow like this:

 {{Rating::where('qr_id', $qr->id)->count()}}

But I want to do it somehow like this in the foreach loop

 {{ $Qr->rating->count() }}

If this is somehow possible.

I get the relation, if I just output the first() of Qr and then var_dump($qrs->ratings->toArray())

But I don't know how to get the count Number of ratings in combination with the foreach loop. Any help would be dearly appreciated.

Couple of things wrong here:

// view:
@foreach($qrs as $qr->rating) 
// should be: 
@foreach($qrs as $qr)

// controller:
$unit = Unit::all()->first();
$qrs = Qr::all()->first();
// this way you get all Units then fetch first Unit from the collection,
// the same with Qrs, so change it to:
$unit = Unit::all(); // do you need it at all?
$qrs = Qr::with('ratings')->get();

This will solve the problem and in the foreach loop you will be able to access $qr->ratings->count() which will be Collection method.

At first you have used this:

@foreach($qrs as $qr->ratings)

You need to change it to this (as already stated in an answer):

@foreach($qrs as $qr)

Then in your index method you have used this:

public function index()
{
    $unit = Unit::all()->first();
    $qrs = Qr::all()->first();
    return View::make('index')->with('unit', $unit)->with('qrs', $qrs);
}

In this case you need to get a collection of QR models and since Unit and Rating are related to Qr then you may use with and get() to get a collection of QR models like this:

public function index()
{
    $qrs = Qr::with(array('unit', 'ratings'))->get();
    return View::make('index')->with('qrs', $qrs);
}

Then you'll be able to loop the Qr models in your view like this:

@foreach($qrs as $qr)
    <tr>
        <td>{{ $qr->id }}</td>
        <td>{{ $qr->unit_id }}</td>
        <td>{{ $qr->ratings->count() }}</td>
    </tr>
@endforeach