<?php

use IlluminateSupportFacadesSchema;
use IlluminateDatabaseSchemaBlueprint;
use IlluminateDatabaseMigrationsMigration;

class CreateOrderProductTable extends Migration
{
/**
 * Run the migrations.
 *
 * @return void
 */
public function up()
{
    Schema::create('order_product', function (Blueprint $table) {
        $table->integer('order_id');
        $table->integer('product_id');
        $table->float('price');
        $table->integer('amount');
        $table->primary(array('order_id', 'product_id'));
        $table->timestamps();
    });
}

/**
 * Reverse the migrations.
 *
 * @return void
 */
public function down()
{
    Schema::dropIfExists('orders_products');
}
}

<?php

namespace App;

use IlluminateDatabaseEloquentModel;

class Product extends Model
{
protected $fillable = ['name', 'price', 'stock', 'short_description', 'long_description'];

public function orders() {
    return $this->belongsToMany('Order', 'order_product', 'product_id', 'order_id');
}

public function carts() {
    return $this->belongsToMany('Cart', 'cart_product', 'product_id', 'cart_id');
}
}

public function destroy($id)
{
    if ($this->validateID($id)) {
        $product = Product::find($id);
        //$product->carts()->detach(); --THE PROBLEMATIC LINE
        Product::destroy($id);
    }
    Session::flash('success', $product->name.' has been succesfully deleted.');
    return redirect()->to('/products');
}