Laravel 6 - `Undefined variable: value` only error

问题:

In the first time I want to save data to database from table this error appear.

ErrorException Undefined variable: value

so I have to manually input the data from tinker or mysql

My Controller

public function store(Request $request)

{

    $validateData = $request->validate([

        'name_device_type' => 'required|max:255',

        'signature' => 'Nullable'

    ]);



    $id = DeviceType::getidDeviceTypes();

    foreach ($id as $value);   // Error happend in this line.

    $lastdevicetypeId = $value->id;

    $newdevicetypeId = $lastdevicetypeId + 1;

    $GetnewdevicetypeId = sprintf('DT%04d', $newdevicetypeId);



    $devicetypes = new DeviceType();

    $devicetypes->idDeviceType = $GetnewdevicetypeId;

    $devicetypes->name_device_type = $request->input('name_device_type');

    $devicetypes->signature = $request->input('signature');

    $devicetypes->save();



    return redirect('/devicetypes')->with('success', 'New Device Type is added');

}

My Migration table

public function up()
    {
        Schema::create('device_types', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->string('idDeviceType');
            $table->string('name_device_type');
            $table->mediumText('signature');
            $table->timestamps();
        });
    }

My create.blade.php

{!! Form::open(['action' => 'DeviceTypesController@store', 'method' => 'POST']) !!}
        <div class="form-group">
            {!! Form::label('name_device_type', 'Type Device'); !!}
            {!! Form::text('name_device_type', '', ['class' => 'form-control', 'placeholder' => 'Type Device']); !!}
        </div>
        <div class="form-group">
            {!! Form::label('signature', 'Signature (Optional)'); !!}
            {!! Form::textarea('signature', '', ['id' => 'classic-ckeditor5', 'class' => 'form-control', 'placeholder' => 'Signature']); !!}
        </div>
        {{ Form::button('<i class="far fa-save"></i> Submit', ['type' => 'submit', 'class' => 'btn btn-info'] )  }}
    {!! Form::close() !!}

the Model

class DeviceType extends Model
{
    // Table Name
    protected $table = 'device_types';
    // Primary Key
    protected $primaryKey = 'idDeviceTypes';
    // Timestamps
    public $timestamps = true;

    public $incrementing = false;

    public static function getidDeviceType(){
        return $getidDeviceType = DB::table('device_types')->orderBy('id','desc')->take(1)->get();
    }
}

But if the table has data this error disappear, also this error will appear again if I remove every data and made the table empty.

回答1:

You could grab the max 'id' of the table and add 1 to it without having to grab a whole record:

...
// validation

$newdevicetypeId = DeviceType::max('id') + 1;

$GetnewdevicetypeId = sprintf('DT%04d', $newdevicetypeId);

// new DeviceType
...

There is the option of having a model event that can set this particular field after the record has been created so it has its own id to use.

回答2:

You have a Semicolon right after the foreach loop definition: foreach ($id as $value); and you are using the $value in the next line $lastdevicetypeId = $value->id; which is outside the scope of your loop.

You should remove the ; following the the foreach loop and change it to : and add a endforeach; where you want to end the loop.

Example:

foreach ($id as $value):
    $lastdevicetypeId = $value->id;
    $newdevicetypeId = $lastdevicetypeId + 1;
    $GetnewdevicetypeId = sprintf('DT%04d', $newdevicetypeId);

    $devicetypes = new DeviceType();
    $devicetypes->idDeviceType = $GetnewdevicetypeId;
    $devicetypes->name_device_type = $request->input('name_device_type');
    $devicetypes->signature = $request->input('signature');
    $devicetypes->save();
endforeach;

Or you can write this code as:

foreach ($id as $value){
    $lastdevicetypeId = $value->id;
    $newdevicetypeId = $lastdevicetypeId + 1;
    $GetnewdevicetypeId = sprintf('DT%04d', $newdevicetypeId);

    $devicetypes = new DeviceType();
    $devicetypes->idDeviceType = $GetnewdevicetypeId;
    $devicetypes->name_device_type = $request->input('name_device_type');
    $devicetypes->signature = $request->input('signature');
    $devicetypes->save();
}