Duplicate key entry when updating object - mysql

Question

I have a Product object that has multiple Shop objects because a shop can offer the same product at different prices / conditions.
I have an edit view for the products that lists the shops where the product is available.
When I make adjustments to the shops of the product eg. price; I get the error that the shop already exists in the database. I know the product exists, but I need the data to be updated.
SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '1-1' for key 'PRIMARY'
public function update(Request $request, $slug)
{
$product = Product::with('shops', 'type')->where('slug', $slug)->first();
[... snip ...]
$i = 0;
foreach($product->shops as $shop) {
$shop = request('shop');
$product->shops()->attach($product->id, [
'shop_id' => $shop[$i]['id'],
'price' => $shop[$i]['price'],
'url' => $shop[$i]['url']
]);
$i++;
}
$product->save();
return redirect('/'.$slug)->with('success', 'Product has been updated');
}
$product->update(); yields the same result.
EDIT:
Product.php
class Product extends Model
{
protected $appends = ['lowest_price'];
public function shops(){
return $this->belongsToMany('App\Shop')->withPivot('price','url');
}
public function type(){
return $this->belongsTo('App\Type');
}
public function getLowestPriceAttribute()
{
$lowest_price = NULL;
foreach($this->shops as $shop) {
if(is_null($lowest_price)) {
$lowest_price = (double)$shop->pivot->price;
}
if($lowest_price > (double)$shop->pivot->price) {
$lowest_price = (double)$shop->pivot->price;
}
}
return $lowest_price;
}
}
Shop.php
class Shop extends Model
{
//
}
Shop migration
public function up()
{
Schema::create('shops', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
$table->string('url');
$table->string('logo');
$table->timestamps();
});
[... snip ...]
}
EDIT2:
More info about the error:
Illuminate \ Database \ QueryException (23000)
SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '1-1' for key 'PRIMARY' (SQL: insert into `product_shop` (`price`, `product_id`, `shop_id`, `url`) values (500.00, 1, 1, http://test.com))
'CREATE TABLE `products` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`make` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`model` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`description` text COLLATE utf8_unicode_ci NOT NULL,
`image` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`video` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`manufacturer_specs` text COLLATE utf8_unicode_ci NOT NULL,
`top_speed` decimal(8,1) NOT NULL,
`range` decimal(8,1) NOT NULL,
`weight` decimal(8,1) NOT NULL,
`type_id` int(10) unsigned NOT NULL,
`slug` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`lowest_price` decimal(8,1) NOT NULL,
`created_at` timestamp NULL DEFAULT NULL,
`updated_at` timestamp NULL DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `products_slug_unique` (`slug`),
KEY `products_type_id_index` (`type_id`),
CONSTRAINT `products_type_id_foreign` FOREIGN KEY (`type_id`) REFERENCES `types` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci'
'CREATE TABLE `product_shop` (
`product_id` int(10) unsigned NOT NULL,
`shop_id` int(10) unsigned NOT NULL,
`price` decimal(8,2) NOT NULL,
`url` text COLLATE utf8_unicode_ci NOT NULL,
PRIMARY KEY (`product_id`,`shop_id`),
KEY `product_shop_product_id_index` (`product_id`),
KEY `product_shop_shop_id_index` (`shop_id`),
CONSTRAINT `product_shop_product_id_foreign` FOREIGN KEY (`product_id`) REFERENCES `products` (`id`) ON DELETE CASCADE,
CONSTRAINT `product_shop_shop_id_foreign` FOREIGN KEY (`shop_id`) REFERENCES `shops` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci'
'CREATE TABLE `shops` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`url` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`logo` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`created_at` timestamp NULL DEFAULT NULL,
`updated_at` timestamp NULL DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci'
Edit3:
If I click the update button, I get the error even if I didn't change anything

Answer 1

You are trying to add another product-to-shop relation with the same keys, that's why you are seeing the index violation.
Instead of using attach, you can use sync:
$product->shops()->sync(
[
$shop[$i]['id'] => [
'price' => $shop[$i]['price'],
'url' => $shop[$i]['url']
]
], false);
The important part is the second parameter, which disabled detaching the other related items.
You could also use syncWithoutDetaching.
For details see:
Docs
Api