AJStacy AJStacy - 1 year ago 93
PHP Question

Eloquent Many to Many Attach Function sending a Null ID

I have the following code which is attempting to attach a product to a product_slot.

$product_slot = new ProductSlot;
$product_slot = $product_slot->where('type', $slot['id'])->first();

$product = new Product;
$product = $product->where('type', (String)$allowed_product)->first();


I can do a
and both return the following:

array (size=6)
'product_slot_id' => int 1
'type' => string 'breakfastplatter1' (length=17)
'default_product_id' => string 'bigbfhotcakebiscplat_3590' (length=25)
'allow_empty' => int 0
'created_at' => string '2016-08-17 19:04:41' (length=19)
'updated_at' => string '2016-08-17 19:04:41' (length=19)

array (size=7)
'product_id' => int 185
'type' => string 'bigbfhotcakebiscplat_3590' (length=25)
'label' => string 'Big Breakfast with Hot Cakes (Biscuit)' (length=38)
'min_option_slots' => int 0
'max_option_slots' => int 0
'created_at' => string '2016-08-17 19:05:40' (length=19)
'updated_at' => string '2016-08-17 19:05:40' (length=19)

Here is the Product Model relationship:

namespace App;

use Illuminate\Database\Eloquent\Model;

class Product extends Model
protected $fillable = ['type', 'label', 'min_option_slots', 'max_option_slots'];

public function productSlots()
return $this->belongsToMany('App\ProductSlot');

However, when I try to sync these models together I get the following error.

SQLSTATE[23000]: Integrity constraint violation: 1048 Column
'product_id' cannot be null (SQL: insert into

) values (, 1))

Ben Ben
Answer Source

You are using custom primary key names instead of the Laravel convention of using id as the primary key. Try adding this to your models:

class Product {
    public $primaryKey = 'product_id';

class ProductSlot {
    public $primaryKey = 'product_slot_id';

Also note that if you don't follow Laravel conventions, you also sometimes need to specify the non-standard primary keys when defining relationship functions:

public function productSlots()
    return $this->belongsToMany('App\ProductSlot', 'product_slot_id', 'product_id');