How to save ID dropdown's attributes dynamic in laravel livewire component - php

Question

How can I save the ID (primary key) of the dynamic dropdowns in a combined mysql field (1,3,2,1 etc... )
I'm sorry, my english is bad
see image form in blade
field mysql save: combinated varchar(255)
see table price mysql with field for save
View Blade:
<form class="form-horizontal" wire:submit.prevent="storePrecio">
#csrf
#foreach ($product->attributeValues->unique('product_attribute_id') as $av)
<div class="form-group">
<label class="col-md-4 control-label">{{ $av->productAttribute->name }} :</label>
<div class="col-md-4">
<select class="form-control" wire:model="attribute_values.{{ $av->productAttribute->id }}">
#foreach ($av->productAttribute->attributeValues->where('product_id', $product->id) as $pav)
<option value="{{ $pav->id }}">{{ $pav->value }}</option>
#endforeach
</select>
</div>
Component Livewire:
class AdminAddPrecioComponent extends Component
{
// tabla precios
public $product_id;
public $category_id;
public $combination;
public $size;
public $quantity;
public $importe;
//atributos de producto
public $attribute_values = [];
public function storePrecio()
{
$this->validate([
'size' => 'required',
'quantity' => 'required',
'importe' => 'required'
]);
//grabar
$product = Product::where('slug', $this->slug)->first();
$product_id = $product->id;
$category_id = $product->category_id;
//
$precio = new Price();
$precio->category_id = $category_id;
$precio->product_id = $product_id;
$precio->size = $this->size;
$precio->quantity = $this->quantity;
$precio->importe = $this->importe;
//saving ID dropdowns dynamic array
foreach ($this->attribute_values as $key => $attribute_value[]) {
$avalues = explode(",", $attribute_value[]);
foreach ($avalues as $avalue) {
$precio->combination = $avalue[$key]; //NOT WORKING => EMPTY
}
}
$precio->save();
session()->flash('message', 'Precio ha sido creado con exito');
}
public function render()
{
$tamano = Tamano::all();
$cantidad = Cantidad::all();
$product_array = Product::all();
$categoria = Category::all();
$product = Product::where('slug', $this->slug)->first();
return view('livewire.admin.admin-add-precio-component', ['cantidad' => $cantidad, 'tamano' => $tamano, 'product_array' => $product_array, 'product' => $product, 'categoria' => $categoria])->layout('layouts.frontend.base');
}
my table attributes fill dropdowns
see table here