Laravel Model binding many to many realtionship does not populate data - php

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>