laravel枢轴返回null

Question

I am working on a site which using laravel framework. I have two tables with many to many relationship, the table are training and budget , and also a join table budget_training .

in both training and budget model, i define the relation like this;

// in Training model
public function budget(){
   return $this->belongsToMany('Budget')->withPivot('amount');
} 

// in Budget model
public function training(){
   return $this->belongsToMany('Training')->withPivot('amount');
}

why in the view $training->pivot is returning null? what is wrong with the code?

full code

// Budget.php
class Budget extends \Eloquent {

    // Add your validation rules here
    public static $rules = [
        // 'title' => 'required'
    ];

    // Don't forget to fill this array
    protected $fillable = ['name'];

    // public function training(){
    //  return $this->belongsToMany('Training')->withPivot('amount');
    // }

}

// Training.php
class Training extends \Eloquent {

    // Add your validation rules here
    public static $rules = [
        // 'title' => 'required'
    ];

    // Don't forget to fill this array
    protected $fillable = [
        'name',
        'city',
        'province',
        'budget_year',
        's_date',
        'e_date'
    ];

    public function material(){
        return $this->hasMany('Material');
    }

    public function budget(){
        return $this->belongsToMany('Budget')->withPivot('amount');
    }

}

code to insert the data

public function postStore(){
    $validator = Validator::make($data = Input::all(), Training::$rules);

    if ($validator->fails())
    {
        return Redirect::back()->withErrors($validator)->withInput();
    }

    $training = Training::create($data);

    foreach(Input::get('budgets') as $k=>$v){
        preg_match('/(\d)/', $k, $budget_id);
        if(count($budget_id) > 0){
            $budget_training = new BudgetTraining;
            $budget_training->budget_id = $budget_id[0];
            $budget_training->training_id = $training->id;
            $budget_training->amount = str_replace(',', '', $v);
            $budget_training->save();
        }
    }

    return Redirect::to('trainings/index');
}

index.blade.php containing this, $trainings from its controller

@foreach($trainings as $training)
            {{ var_dump($training->pivot) }}
            <tr>
                <td>{{ $training->name }}</td>
                <td>{{ $training->budget_year }}</td>
                <td>{{ $training->city }}, {{ $training->province }}</td>
                <td>{{ $training->s_date }}</td>
                <td>{{ $training->e_date }}</td>
                <td>
                    <a href="{{ url('trainings/edit/'.$training->id) }}" class="btn btn-info"><i class="fa fa-edit"></i></a>
                    <a href="{{ url('trainings/destroy/'.$training->id) }}" class="btn btn-danger"><i class="fa fa-trash-o"></i></a>
                </td>
            </tr>
            @endforeach

here is the index method.

public function getIndex(){
    $trainings = Training::all();

    return View::make('trainings.index', compact('trainings'));
}

Answer 1

You can't access the pivot object of your models because they haven't been joined over the pivot table.

In your code you just select all the training rows from the db without any use of the pivot table. So you have no connection to Budget and therefore no pivot object.

What would work instead would be getting all trainings from one budget like that

$trainings = Budget::find(1)->training;

foreach($trainings as $training){
    var_dump($training->pivot);
}

Or what you probably want is this:

foreach($trainings as $training){
    $budgets = $training->budget;
    foreach($budgets as $budget){
        var_dump($budget->pivot);
    }
}

If you do this make sure you use

$trainings = Training::with('budget')->get();

So it doesn't have to query the db every time you call ->budget on a training

Answer 2

If you want to access pivot data, you can do it this way, for example:

$training = Training->with('budget')->find(1);
echo $training->name;
foreach ($training->budget as $b) {
  echo $b->name.' '.$b->pivot->amount."<br />"
}

So you don't access pivot data on model, but on relation, in this case not:

$training->pivot->amount

but

$training->budget[$i]->pivot->amount

(assuming $i is loop index)