我将Laravel与Resources结合使用来创建REST Api。我想获得一个包含有关关系元素的信息的json，例如示例

{
"id": 30,"calf": 23,"chest": 27
"user_id": {
    "id": 30,"email": "test@example.com"
}}

但是当我在docs中创建代码时，出现错误“在int上调用成员函数first（）”。有人可以告诉我我做错了什么吗？我做了完全一样的事情，就像在文档中一样，我也尝试使用whenLoaded，但是出现了同样的错误。这是我的代码：

 class CircuitMeasurementResource extends JsonResource
{
    /**
     * Transform the resource into an array.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return array
     */
    public function toArray($request)
    {
//        return parent::toArray($request);
        return [
            'id' => $this->id,'calf' => $this->calf,'chest' => $this->chest,'user_id' => UserResource::collection($this->user_id)
        ];
    }
}

我的方法在控制器中显示：

public function show(CircuitMeasurement $circuitMeasurement): CircuitMeasurementResource {
        return new CircuitMeasurementResource($circuitMeasurement);
    }

我的模特：

    class CircuitMeasurement extends Model
{
    protected $fillable = [
        'user_id','calf','thigh','hips','waist','chest','neck','biceps'
    ];
    public function users(){
        return $this->belongsTo(User::class);
    }
}

class User extends Authenticatable
{
    use Notifiable,HasApiTokens;

    /**
     * The attributes that are mass assignable.
     *
     * @var array
     */

    protected $fillable = [
        'name','email','password',];

    /**
     * The attributes that should be hidden for arrays.
     *
     * @var array
     */
    protected $hidden = [
        'password','remember_token',];

    /**
     * The attributes that should be cast to native types.
     *
     * @var array
     */
    protected $casts = [
        'email_verified_at' => 'datetime',];

    public function weightMeasurement(){
        return $this->hasMany(WeightMeasurement::class);
    }
    public function circuitMeasurement(){
        return $this->hasMany(CircuitMeasurement::class);
    }

}