Using allFields() method breaks export of relationship and computed fields

[ahmedabdel3al]

[#48 ]
this PR merge non index fields with index fields when using allFields method

I have case that i want to export all index fields with non index fields. so i found allFields method but this method breaks export of relationship and computed fields .
so i found getOnly method in Only Trait which set only in case of index Fields and count of only equal zero
but also needed to merge non index fields with index fields in case of using allFields method

[patrickbrouwers]

Can you give a couple of examples I can test this against?

[ahmedabdel3al]

@patrickbrouwers
#49
this PR fix this issue

 /**
     * Get the fields displayed by the resource.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return array
     */
    public function fields(Request $request)
    {

        return [
            ID::make()->sortable(),

            Text::make('Downpayment', 'booking_price')->sortable(),

            BelongsTo::make('Show Room', 'showRoom')->sortable(),

            BelongsTo::make('Vehicle Model', 'vehicleModel')->sortable(),

            BelongsTo::make('Vehicle Category', 'vehicleCategory')->sortable(),

            BelongsTo::make('Vehicle Color', 'vehicleColor')->sortable(),

        ];
    }


 /**
     * Get the actions available for the resource.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return array
     */
    public function actions(Request $request)
    {
        return [
            (new DownloadExcel)->withHeadings()->allFields()->except([
                'payment_date',
                'toyota_id',
                'status',
                'payment_method',
                'personal_id_type',
                'show_room_id',
                'vehicle_model_id',
                'vehicle_category_id',
                'vehicle_color_id',

            ]),
        ];
    }

before
the result set not included nova resources attributes

after
the result set will include nova resources attributes with model attributes