返回值必须是 ?Illuminate\\Database\\Query\\Builder, App\\Models\\ModelName 返回的类型

我试图得到以下回应：

"user": {
        "id": 1,
        "first_name": "john",
        "last_name": "doe",
        "email": "[email protected] /cdn-cgi/l/email-protection",
        "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
                    } 
    }

代替：

"user": {
        "id": 1,
        "first_name": "john",
        "last_name": "doe",
        "email": "[email protected] /cdn-cgi/l/email-protection",
        "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
    }

为了做到这一点，我在用户模型中使用了一个 mutator 函数：

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

但是，国家/地区表已在外部数据库中找到，我已正确设置其连接。

但我按照这个创建了国家模型Laravel 文档 https://laravel.com/docs/8.x/eloquent:

use Illuminate\Database\Eloquent\Model;

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',
];
}

当我尝试获取用户时，出现以下错误：

{
"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
}

我试图尽可能多地解释我的情况。 感谢您的帮助。

问题是你在函数中说getCountryIdAttribute它返回Builder | null。当你这样做时

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

它将返回一个实例Country or null。要解决您的问题，您应该将返回类型更新为Country | null:

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

Laravel 提供了使用的方法关系 https://laravel.com/docs/8.x/eloquent-relationships#one-to-one这将极大地提高您的代码性能。在这种情况下你可以这样做：

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

然后在获取时users你可以做：

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

这将阻止您的代码N+1 https://medium.com/doctolib/understanding-and-fixing-n-1-query-30623109fe89#:%7E:text=TL%3BDR%3A%20The%20N%2B,%E2%80%9CHow%20to%20fix%20it%3F%E2%80%9D问题。