Laravel模型与自身的关系

Question

我正在尝试在一个表中使用父/子关系。每个资产都属于父资产，这是资产表/资产模型中的另一个资产。

任务表中的每个任务都有一个asset_id记录，而由该ID标识的资产在其记录中具有parent_asset_id。我试图访问任务中使用的资产的父级的名称字段，我收到一个错误。以下是涉及的代码：

这是资产模型中的关系：

public function parent_asset()
   {
     return $this->belongsTo('\pmms\Asset', 'parent_asset_id');
   }

和任务模型中的关系

  public function asset()
   {
     return $this->belongsTo('\pmms\Asset');
   }

Ina刀片文件我试图访问资产表中的名称字段，如下所示：

$task->asset->parent_asset->name

但是我收到了错误：

Trying to get property of non-object (View: C:\pmms\resources\views\partials\tasklist.blade.php)

我在哪里错了？

{{dd（$ asset-＆gt; parent_asset（））}}的结果：

  BelongsTo {#657 ▼
  #foreignKey: "parent_asset_id"
  #otherKey: "id"
  #relation: "parent_asset"
  #query: Builder {#663 ▶}
  #parent: Asset {#664 ▼
    #dates: array:1 [▶]
    #fillable: array:19 [▶]
    #connection: null
    #table: null
    #primaryKey: "id"
    #perPage: 15
    +incrementing: true
    +timestamps: true
    #attributes: array:24 [▼
      "id" => 4
      "agency_id" => 1
      "name" => "Bedrock Park"
      "description" => ""
      "serial_number" => ""
      "asset_category_id" => 5
      "activity_center_id" => 1
      "original_cost" => 0.0
      "in_service_date" => "1920-01-01"
      "expected_lifespan" => 0
      "status" => 1
      "notes" => ""
      "created_at" => "2015-09-14 17:59:47"
      "updated_at" => "2016-10-31 20:01:29"
      "square_feet" => 0
      "gps_longitude" => "0.000000"
      "gps_latitude" => "0.000000"
      "parent_asset_id" => 0
      "supervisor_id" => 0
      "model_number" => 0
      "is_location" => 1
      "asset_sub_category_id" => 0
      "asset_group_id" => 2
      "address" => ""
    ]
    #original: array:24 [▶]
    #relations: []
    #hidden: []
    #visible: []
    #appends: []
    #guarded: array:1 [▶]
    #casts: []
    #touches: []
    #observables: []
    #with: []
    #morphClass: null
    +exists: true
  }
  #related: Asset {#682 ▶}
}

刀片模板代码：

<div class="whitebox">

        @forelse ($tasks as $task)
            @if($last_multi_asset_id == 0 or $last_multi_asset_id != $task->multi_asset_task_id)

                <?php 
                if ($task->sourceable_type == '\pmms\Work_order') {
                    $notes = $task->sourceable->explanation;
                } else {                    
                    $notes = $task->supervisor_notes;
                }                       
                ?>

                    <div class="outstanding-task-accordion-div @if ($task->status == 1)status-in-process @elseif ($task->status == 2)status-competed @endif">
                        <a href="#" data-toggle="modal" data-target="#taskModal{!! $i !!}">
                            <div class="panel-title-accordion">                     
                                @if($tasklist_type == 'o' && $tasklist_personal != 1) <div class="col-md-2 task-header-staff">{!! $task->assignee->userName() !!} 
                                    @if(!is_null($task->crew_assignment_id)) <span class="crew text-nowrap">(Crew {!! $task->crew_assignment->id !!})</span> @endif</div> @endif
                                    <div class="col-md-1 col-sm-2 task-header-date text-nowrap"> {!! $task->do_date->format('n/j/Y') !!}</div>
                                    <div class="col-md-2 col-sm-3 task-header-asset">@if($task->multi_asset_task_id > 0) Multi-Asset Task @else {!! $task->asset->name !!} - {!! $task->asset->parent_asset->name !!} 
                                @endif
                                @if(!is_null($task->crew_assignment_id)) <span class="crew text-nowrap">Crew {!! $task->crew_assignment->id !!}</span> @endif</div>
                                <div class="col-md-4 col-sm-3 task-header-task">{!! $task->sourceable->name !!}</div>
                                <div class="col-md-1 col-sm-1 task-header-priority-level text-nowrap">Priority: {!! $task->priority_level !!}</div>
                                <div class="col-md-1 col-sm-1 task-header-hours text-nowrap">Hours: {!! $task->hours !!}</div>
                                <div class="col-md-1 col-sm-1 task-header-status text-nowrap">{!! $task->status_text() !!}</div>
                            </div>
                        </a>

                    </div>
                    <div class="clear-both"></div>

                        <!-- Inside of panel -->
                        @if ($task->multi_asset_task_id > 0)
                            @include('partials.tasklist_accordion_multi')
                        @else
                            @include('partials.tasklist_accordion_indi')
                        @endif
                        <!-- End inside of panel -->


                <?php 
                    $i++;
                    $last_multi_asset_id = $task->multi_asset_task_id;
                ?>
            @endif <!-- Ends the multi_asset if  -->
        @empty
            @if (isset($staff))
                There are no {!! $text !!} tasks for {!! $staff['first_name'] !!} {!! $staff['last_name'] !!} {!! $text2 !!}. 
            @else
                There are no tasks.
            @endif
        @endforelse

</div>