Laravel多对多

本文介绍了Laravel多对多 - - 意外结果集 - > select（）的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 我不知道有没有人可以帮助，因为我已经打了墙，还在学习Laravel ORM。任何人都可以解释为什么，当我运行：

public function locationTags（）{ return $ this-> hasMany （'App\UserHasLocationTags'，'user_id'） - > join（'location_tags AS lt'，'lt.id'，'='，'location_tag_id'）; }

我得到这个结果集：（snipped ...）

{id：1，created_at：2015-05-13 13:04:56 ，updated_at：2015-05-13 13:04:56，email：REMOVED，firstname：REMOVED，lastname：REMOVED，location_id：0，deleted_at：null，permissions：[]，location_tags b $ b {user_id：1，location_tag_id：1，id：1，created_at：2015-05-13 13： 06:28，updated_at：2015-05-13 13:06:28，name：Test Tag 0，location_id deleted_at：null }， {user_id：1，location_tag_id：2，id created_at：2015-05-13 11:40:21，updated_at：2015-05-13 12:56:13， name：Test Tag 123，location_id：1，deleted_at：null } ] }

哪个是ace！但是，当我开始从location_tags加入中选择我想要的列时，使用：

public function locationTags（）{ return $ this-> hasMany（'App\UserHasLocationTags'，'user_id'） - > join（'location_tags AS lt'，'lt.id'，'='，'location_tag_id'） - > select（'lt.id'，'lt.name'）; }

我最终结论：

{id：1，created_at：2015-05-13 13:04:56， updated_at：2015-05-13 13:04:56，email：REMOVED，firstname：REMOVED，lastname：REMOVED ，location_id：0，deleted_at：null，permissions：[]，location_tags：[] }

有人可以解释发生了什么吗？并且可能指向正确的方向限制选择？谢谢！

更新 我也试过：

$ query = \App\User :: with（['permissions'，'locationTags'=> function（$ query）{ $ query-> select 'lt.id'，'lt.name'）; }]）;

哪个返回相同的结果：（

解决方案

此处的关键是您必须包含一个 select（） Laravel可以使用至少一个键来映射结果集，在我的情况下，它是 user_id ，如下所示：

public function locationTags（）{ return $ this-> hasMany（'App\UserHasLocationTags'，'user_id'） - > join（'location_tags （'user_id'，'lt.name'，'location_tag_id'）; }

然后返回一个更好的结果集：

{id：1，created_at：2015-05-13 13:04:56，updated_at 2015-05-13 13:04:56，email：REMOVED，firstname：REMOVED，lastname：REMOVED，location_id：0，deleted_at：null，permissions：[]，location_tags：[ {user_id：1，name ：Test Tag 0，location_tag_id：1 }， {user_id：1，name：Test Tag 123 ，location_tag_id：2 } ] }

希望这有助于有人在未来，因为它让我猜测好几个小时。

I wonder if anyone can help, as I've hit a wall and still learning Laravel ORM. Can anyone explain why, when I run:

public function locationTags(){ return $this->hasMany('App\UserHasLocationTags', 'user_id') ->join('location_tags AS lt', 'lt.id', '=', 'location_tag_id'); }

I get this result set: (snipped...)

{ "id": 1, "created_at": "2015-05-13 13:04:56", "updated_at": "2015-05-13 13:04:56", "email": "REMOVED", "firstname": "REMOVED", "lastname": "REMOVED", "location_id": 0, "deleted_at": null, "permissions": [], "location_tags": [ { "user_id": 1, "location_tag_id": 1, "id": 1, "created_at": "2015-05-13 13:06:28", "updated_at": "2015-05-13 13:06:28", "name": "Test Tag 0", "location_id": 1, "deleted_at": null }, { "user_id": 1, "location_tag_id": 2, "id": 2, "created_at": "2015-05-13 11:40:21", "updated_at": "2015-05-13 12:56:13", "name": "Test Tag 123", "location_id": 1, "deleted_at": null } ] }

Which is ace! However, when I start to select the columns I want from the location_tags join, with:

public function locationTags(){ return $this->hasMany('App\UserHasLocationTags', 'user_id') ->join('location_tags AS lt', 'lt.id', '=', 'location_tag_id') ->select('lt.id', 'lt.name'); }

I end up with:

{ "id": 1, "created_at": "2015-05-13 13:04:56", "updated_at": "2015-05-13 13:04:56", "email": "REMOVED", "firstname": "REMOVED", "lastname": "REMOVED", "location_id": 0, "deleted_at": null, "permissions": [], "location_tags": [] }

Can someone explain what's going on? And possibly point me in the right direction to limit the selects? Thanks!

Update I've also tried:

$query = \App\User::with(['permissions', 'locationTags' => function($query){ $query->select('lt.id', 'lt.name'); }]);

Which returns the same result :(

解决方案

Figured it out. The key here was that you must include a select() value of at least one key that Laravel can use to map the result set. In my case it was user_id, like so:

public function locationTags(){ return $this->hasMany('App\UserHasLocationTags', 'user_id') ->join('location_tags AS lt', 'lt.id', '=', 'location_tag_id') ->select('user_id', 'lt.name', 'location_tag_id'); }

Which then returns a much nicer results set:

{ "id": 1, "created_at": "2015-05-13 13:04:56", "updated_at": "2015-05-13 13:04:56", "email": "REMOVED", "firstname": "REMOVED", "lastname": "REMOVED", "location_id": 0, "deleted_at": null, "permissions": [], "location_tags": [ { "user_id": 1, "name": "Test Tag 0", "location_tag_id": 1 }, { "user_id": 1, "name": "Test Tag 123", "location_tag_id": 2 } ] }

Hope this helps someone out in the future, because it kept me guessing for a good couple of hours.