试图获取非对象的属性-Laravel 5

我正在尝试在文章中回显用户的名称，并且得到ErrorException: Trying to get property of non-object。我的代码：

楷模

1. News

    class News extends Model
    {
      public function postedBy()
      {
         return $this->belongsTo('App\User');
      }
      protected $table = 'news';
      protected $fillable = ['newsContent', 'newsTitle', 'postedBy'];
    }

2. User

    class User extends Model implements AuthenticatableContract,
                                AuthorizableContract,
                                CanResetPasswordContract
    {
        use Authenticatable, Authorizable, CanResetPassword;

        protected $table = 'users';

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

        protected $hidden = ['password', 'remember_token'];

    }

架构图

表 users

表 news

控制者

public function showArticle($slug)
    {
        $article = News::where('slug', $slug)->firstOrFail();
        return view('article', compact('article'));
    }

刀

{{ $article->postedBy->name }}

当我尝试删除刀片中的名称时，{{ $article->postedBy }}它会输出id，但是当我尝试在其中添加-> name时，会显示，Trying to get property of non-object但name我的表和User模型中都有一个字段。我想念什么吗？