Laravel：使用Eloquent ORM的N到N（mysql）关系(Laravel: N to N (mysql) relation using Eloquent ORM)

 我有4张桌子： 
 
// Table countries
+----+------+
| Id | Name |
+----+------+
|  1 | USA  |
|  2 | GB   |
+----+------+

// Table platforms
+----+---------+
| Id |  Name   |
+----+---------+
|  1 | Windows |
|  2 | Linux   |
+----+---------+

// Table users
+----+-------+------------+-------------+
| Id | Name  | country_id | platform_id |
+----+-------+------------+-------------+
|  1 | Admin |          1 |           1 |
|  2 | Test  |          2 |           1 |
+----+-------+------------+-------------+

// Table posts
+----+-----------+------------+-------------+---------+
| Id |   Title   | country_id | platform_id | user_id |
+----+-----------+------------+-------------+---------+
|  1 | TestPost1 |          2 |           1 | 1       |
|  2 | TestPost2 |          2 |           2 | null    |
+----+-----------+------------+-------------+---------+
 
 数据库应该能够实现以下关系： 
 
 
 
 用户（N）< - >（N）平台 
 
 
 用户（N）< - >（N）国家 
 
 
 用户（0..1）< - >（N）发布 
 
 
 邮政（N）< - >（N）国家 
 
 
 发布（N）< - >（1）平台 
 
 
 所以现在我尝试在Laravel Eloquent ORM文档之后实现这些关系： 
 
  // Country.php
  public function posts()
  {
      return $this->belongsToMany('App\Post');
  }

  public function users()
  {
      return $this->belongsToMany('App\User');
  }

  // Platform.php
  public function users()
  {
      return $this->belongsToMany('App\User');
  }

  public function posts()
  {
      return $this->belongsToMany('App\Post');
  }

  // User.php
  public function posts()
    {
        return $this->hasMany('App\Post');
    }

    public function countries()
    {
        return $this->hasMany('App\Country');
    }

    public function platforms()
    {
          return $this->hasMany('App\Platform');
    }

  // Post.php
  public function countries()
  {
      return $this->hasMany('App\Country');
  }

  public function platforms()
  {
      return $this->hasMany('App\Comment');
  }

  public function user()
  {
      return $this->belongsTo('App\User', 'user_id');
  }
 
 但现在我很困惑，因为我认为在mysql中实现N到N关系的方法是向db添加第三个表，例如： 
 
// Table CountryUserRelations to implement User (N) <-> (N) Country
+----+------------+---------+
| Id | country_id | user_id |
+----+------------+---------+
|  1 |          1 |       1 |
|  2 |          2 |       1 |
|  3 |          1 |       2 |
|  4 |          2 |       2 |
+----+------------+---------+
 
 但是Eloquent ORM如何处理我模型中的规则？ 它是否会保持N到N的关系而不必添加关系表？ 或者我错过了什么或误解了雄辩的ORM关系概念？ 

I got 4 tables:
 
// Table countries
+----+------+
| Id | Name |
+----+------+
|  1 | USA  |
|  2 | GB   |
+----+------+

// Table platforms
+----+---------+
| Id |  Name   |
+----+---------+
|  1 | Windows |
|  2 | Linux   |
+----+---------+

// Table users
+----+-------+------------+-------------+
| Id | Name  | country_id | platform_id |
+----+-------+------------+-------------+
|  1 | Admin |          1 |           1 |
|  2 | Test  |          2 |           1 |
+----+-------+------------+-------------+

// Table posts
+----+-----------+------------+-------------+---------+
| Id |   Title   | country_id | platform_id | user_id |
+----+-----------+------------+-------------+---------+
|  1 | TestPost1 |          2 |           1 | 1       |
|  2 | TestPost2 |          2 |           2 | null    |
+----+-----------+------------+-------------+---------+
 
The database should be able to implement the following relations:
 
 
 
User (N) <-> (N) Platform
 
 
User (N) <-> (N) Country
 
 
User (0..1) <-> (N) Post
 
 
Post (N) <-> (N) Country
 
 
Post (N) <-> (1) Platform
 
 
So now I tried to implement these relations following Laravel Eloquent ORM documentation: 
 
  // Country.php
  public function posts()
  {
      return $this->belongsToMany('App\Post');
  }

  public function users()
  {
      return $this->belongsToMany('App\User');
  }

  // Platform.php
  public function users()
  {
      return $this->belongsToMany('App\User');
  }

  public function posts()
  {
      return $this->belongsToMany('App\Post');
  }

  // User.php
  public function posts()
    {
        return $this->hasMany('App\Post');
    }

    public function countries()
    {
        return $this->hasMany('App\Country');
    }

    public function platforms()
    {
          return $this->hasMany('App\Platform');
    }

  // Post.php
  public function countries()
  {
      return $this->hasMany('App\Country');
  }

  public function platforms()
  {
      return $this->hasMany('App\Comment');
  }

  public function user()
  {
      return $this->belongsTo('App\User', 'user_id');
  }
 
But now I am confused, as I thought the way to implement N to N relations in mysql is to add a third table to db, for example like that:
 
// Table CountryUserRelations to implement User (N) <-> (N) Country
+----+------------+---------+
| Id | country_id | user_id |
+----+------------+---------+
|  1 |          1 |       1 |
|  2 |          2 |       1 |
|  3 |          1 |       2 |
|  4 |          2 |       2 |
+----+------------+---------+
 
But how does Eloquent ORM handle the rules inside my model? Will it keep the N to N relations without having to add a relations table? Or am I missing something or misunderstanding the Eloquent ORM Relations concept?

原文：https://stackoverflow.com/questions/43416437