Return value must be of type ?Illuminate\Database\Query\Builder, App\Models\ModelName returned

I’m trying to have the following response:

"user": {
        "id": 1,
        "first_name": "john",
        "last_name": "doe",
        "email": "[e-mail]",
        "phone_number": "12345678",
        "email_verified_at": null,
        "created_at": "2021-09-02T08:57:07.000000Z",
        "updated_at": "2021-09-02T08:57:07.000000Z",
        "country": {
                     "id": 1,
                     "name": "UK",
                     "phone_code": 44
                    } 
    }

Instead of:

"user": {
        "id": 1,
        "first_name": "john",
        "last_name": "doe",
        "email": "[e-mail]",
        "phone_number": "12345678",
        "email_verified_at": null,
        "created_at": "2021-09-02T08:57:07.000000Z",
        "updated_at": "2021-09-02T08:57:07.000000Z",
        "country_id": 1
    }

In order to do that, I am using a mutator function inside the User Model:

public function getCountryIdAttribute(): Builder|null
{
   return Country::where('id', $this->attributes['country_id'])
    ->get()
    ->first();
}

However, the countries table is already found in an external database which I set up its connection properly.

But I created the Country Model following this Laravel documentation:

use IlluminateDatabaseEloquentModel;

class Country extends Model
{
/**
 * The database connection that should be used by the model.
 *
 * @var string
 */
protected $connection = 'my second db connection name';

/**
 * The table associated with the model.
 *
 * @var string
 */
protected $table = 'countries';

/**
 * The primary key associated with the table.
 *
 * @var string
 */
protected $primaryKey = 'id';

/**
 * The model's default values for attributes.
 *
 * @var array
 */
protected $attributes = [
    'id',
    'name',
    'phone_code',
];
}

When I am trying to fetch the user I get the following error:

{
"error": [
    "App\Models\User::getCountryIdAttribute(): Return value must be of type ? 
    Illuminate\Database\Query\Builder, App\Models\Country returned"
],
"message": "Unhandled server exception",
"code": 500
}

I tried to explain my case as much as possible. Thank you for your help.

Answer

The problem is that you are saying in the function getCountryIdAttribute it returns Builder | null. When you do

   return Country::where('id', $this->attributes['country_id'])
    ->get()
    ->first();

It will return an instance of Country or null. To fix your problem you should update your return type to Country | null:

public function getCountryIdAttribute(): Country | null
{
   return Country::where('id', $this->attributes['country_id'])
    ->get()
    ->first();
}

---

Laravel provides ways to work with relationships that will greatly improve your code performance. In this case you can do:

public function country()
{
  return $this->hasOne(Country::class, 'country_id');
}

Then when fetching the users you can do:

$users = User::where(...)->with('country')->get();

This will prevent your code from having N+1 problems.