Laravel Model将多对多绑定绑定不会填充数据

Question

I have two tables with a many to many relation (Project and Center, the pivot table is ProjectCenter).

These are my models:

Project:

class Project extends Model {
    public function centers()
    {
        return $this->belongsToMany('App\Models\Center', 'ProjectCenter', 'IDProject', 'IDCenter');
    }
    public function getCenterListAttribute()
    {
        return $this->centers->lists('IDCenter')->all();
    }
}

Center:

class Center extends Model {
    public function projects()
    {
        return $this->belongsToMany('App\Models\Project', 'ProjectCenter', 'IDCenter', 'IDProject');
    }
}

Controller -> edit:

public function edit($id)
    {
        $project = Project::find($id);
        $centerList = Center::lists('Name', 'IDCenter')->toArray();
        return view('project/add', array('centerList' => $centerList))->with('project', $project);
    }

And the view:

{!! Form::label('centers_list', 'Center*') !!}
{!! Form::select('centers_list[]', 
    $centerList, 
    null, 
    array(
        'class' => 'form-control ', 
        'required' => 'required', 
        'multiple' => true, 
        'data-placeholder' => 
        'Select a center'
   )
 ) !!}

But I can not select the data already stored previously.

For example: the project 8 (IDProject) has two centers (1 and 2) but the data is not populated in the multiple select:

What am I doing wrong?

Answer 1

You all time get same result $centerList = Center::lists('Name', 'IDCenter')->toArray(); but you must be get product centers using query with model.

$project = Project::with("centers:Name,IDCenter")->find($id);
$centerList = $project->centers->pluck('Name', 'IDCenter')->toArray();

Answer 2

I already solve the problem using a foreach to select the related centers:

<select multiple="multiple" name="centers[]" id="centers" class="form-control select2" required="required" data-placeholder="Select a center">
 @if($centerList)
  @foreach($centerList as $key => $center)
    <option value="{{$key}}" {{ (collect($selectedCenters)->contains($key)) ? "selected='selected'" : ''  }} >{{$center}}</option>
  @endforeach
 @endif
</select>