Question

我在多对多插入中遇到麻烦。我在控制器中的代码是正确的。添加成功的两个数据后，第三次尝试插入会产生错误：

以null调用成员函数bagcollects（）

并且错误在此代码上

$collection->bagcollects()->attach($bagcollect->id);

我只是不明白为什么会发生此错误！

我将展示CollectionsController存储方法的整个代码：

public function addbag(Request $request){
    $collection = Collection::find($request->input('collection_id'));
    $bagcollect = Bagcollect::create([
        'bag_id' => $request->input('bag_id'),
        'weight' => $request->input('weight')
    ]);
    $collection->bagcollects()->attach($bagcollect->id);
    return redirect()->route('collections.show', ['collection'=> $collection->id]);
}

迁移收藏集

Schema::disableForeignKeyConstraints();
if(!Schema::hasTable('collections')){
    Schema::create('collections', function (Blueprint $table) {
        $table->engine = "InnoDB";
        $table->increments('id');
        $table->integer('assignment_id')->unsigned();
        $table->foreign('assignment_id')->references('id')->on('assignments')->onUpdate('cascade')->onDelete('cascade');
        $table->timestamp('collected_on');
    });
}

迁移bagcollects

Schema::create('bagcollects', function (Blueprint $table) {
    $table->engine = "InnoDB";
    $table->increments('id');
    $table->integer('bag_id')->unsigned();
    $table->double('weight', 8, 2);
    $table->foreign('bag_id')->references('id')->on('bags');
    $table->timestamps();
});

迁移bagcollect_collection

Schema::create('bagcollect_collection', function (Blueprint $table) {
    $table->engine = "InnoDB";
    $table->increments('id');
    $table->integer('bagcollect_id')->unsigned();
    $table->integer('collection_id')->unsigned();
    $table->foreign('bagcollect_id')->references('id')->on('bagcollects');
    $table->foreign('collection_id')->references('id')->on('collections');
    $table->timestamps();
});

集合show.blade.php添加模式

<!-- ADD MODAL -->
<div class="modal fade" role="dialog" id="addModal">
    <div class="modal-dialog">
        <div class="modal-content">
            <div class="modal-header">
                <button type="button" class="close" data-dismiss="modal">&times;</button>
                <h4 class="modal-title">New Collection</h4>
            </div>

            <div class="modal-body">
                <div class="row">
                    <div class="col-md-12"> 
                        <form class="form-horizontal" method="POST" action="{{ route('collections.addbag') }}">
                            {{ csrf_field() }}


                            <div class="row form-group">  

                                <input class="form-control" name = "collection_id" id="collection_id" value="{{$collection->id}}" type="hidden">
                                 <div class="{{ $errors->has('bag') ? ' has-error' : '' }}">
                                        <div class="col-md-8">
                                            <label for="bag_id">Bag</label>
                                             <select class="form-control" required id="bag" name="bag_id">
                                                 <option value="" data-hidden="true"  
                                                    selected="selected">
                                                </option>
                                                    @foreach($bags as $bag)
                                                        <option value= "{{ $bag->id }}">
                                                              {{ $bag->name }} 
                                                        </option>
                                                    @endforeach
                                              </select>
                                        </div>
                                    </div>

                                  <div class="{{ $errors->has('weight') ? ' has-error' : '' }}">
                                        <div class="col-md-8">
                                            <label for="weight">Weight</label>
                                             <input type="text" class="form-control" id="weight" name= "weight" required>
                                        </div>
                                  </div>

                            </div>   

                            <!-- SUBMIT BUTTON -->
                            <button type="submit" class="btn btn-success btn-fill pull-right" id="form-button-add">
                                Create
                            </button>

                            <button  data-dismiss="modal" aria-hidden="true" class="btn btn-basic pull-right" style="margin-right: 2%">
                                Cancel
                            </button>             
                            <div class="clearfix"></div>

                        </form>                
                    </div>
                </div>
            </div>
        </div>
    </div>
</div>

Collection.php模型

protected $fillable = [
    'id',
    'assignment_id',
    'bag_id'
];

public $timestamps = false;

public function assignment()
{
    return $this->belongsTo('App\Assignment');
}

public function bagcollects()
{
    return $this->belongsToMany('App\Bagcollect');
}

Bagcollect.php

protected $fillable = [
    'bag_id',
    'weight'
];

public function collections()
{
    return $this->belongsToMany('App\Collection');
}

public function bag()
{
    return $this->belongsTo('App\Bag');
}

BagcollectCollection.php

protected $table = "bagcollect_collection";

protected $fillable = [
    'bagcollect_id',
    'collection_id',

];

Answer 1

在null上调用成员函数...

表示您正在尝试在null对象上调用函数。查看您的代码：

$collection = Collection::find($request->input('collection_id'));

根据您当前的逻辑，$collection可能是null，因此调用

$collection->bagcollects() ...

将抛出此错误。

调试Collection::find(...)的结果，并确保$collection不是null。

多对多插入错误调用成员函数Laravel 5.5

1 个答案: