Laravel 5 SQL连接3个表但返回null

Question

我有3张桌子。

1. 名称：目录

2. 名称： Directory_relations

3. 姓名：视频

   

我的问题是当我想要加入3个表时。因为当我使用Directory_relations加入Directory时，它显示正确但只有文件夹，但是当我加入vidoes时，什么都不显示。有可能显示所有这些。

在下面的代码中，错过ROW在文件夹3中使用VIDEO_ID。

array:1 [▼
      0 => array:9 [▼
        "id" => "4"
        "video_id" => "0"
        "directory_id" => "4"
        "parent_id" => "0"
        "created_at" => "-0001-11-30 00:00:00"
        "updated_at" => "-0001-11-30 00:00:00"
        "name" => "Folder2"
        "user_id" => "265"
        "children" => array:2 [▼
          0 => array:9 [▼
            "id" => "5"
            "video_id" => "0"
            "directory_id" => "5"
            "parent_id" => "4"
            "created_at" => "-0001-11-30 00:00:00"
            "updated_at" => "-0001-11-30 00:00:00"
            "name" => "Folder3"
            "user_id" => "265"
            "children" => array:1 [▼
              0 => array:8 [▼
                "id" => "7"
                "video_id" => "0"
                "directory_id" => "7"
                "parent_id" => "5"
                "created_at" => "-0001-11-30 00:00:00"
                "updated_at" => "-0001-11-30 00:00:00"
                "name" => "Folder33"
                "user_id" => "265"
              ]
            ]
          ]
          1 => array:8 [▼
            "id" => "6"
            "video_id" => "0"
            "directory_id" => "6"
            "parent_id" => "4"
            "created_at" => "-0001-11-30 00:00:00"
            "updated_at" => "-0001-11-30 00:00:00"
            "name" => "Folder22"
            "user_id" => "265"
          ]
        ]
      ]
    ]

有2个连接（带文件夹）仅显示没有视频的文件夹：

$dir = Directory::select('directory_relations.*','directory.*')->join('directory_relations', 'directory_relations.directory_id', '=', 'directory.id')->where('user_id',Auth::user()->id)->get();

有3个连接（文件夹+视频）没有显示任何内容：     $ dir = Directory::select('directory_relations.*','directory.*','videos.*')->join('directory_relations', 'directory_relations.directory_id', '=', 'directory.id')->join('videos', 'directory_relations.video_id', '=', 'videos.id')->where('directory.user_id',Auth::user()->id)->get();