Learn Laravel5's Eloquent relationship

Eloquent是Laravel的原始ActiveRecord是实现的，建立在Laravel的Fluent Query Builder之上的，所以Eloquent类和Fluent类是一样的，能实现复杂的SQL语句和非常直观表达出的表与表之间的关系。本文就以此展开学习，希望对大家有所帮助。

一个用户可能有多个文章，一个文章是某个用户书写的，这就是关系。同样文章中可能包含多个 TAG，而一个 TAG 可能关联多个文章。

在项目中，我们已经有了 User.php，也就是用户模型，查看一下，相当简单。我们希望直接使用 $user->articles() 的形式获取全部文章，让我们修改 user 模型：

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

但是我们仅仅完成了关系中的一端，让我们来处理另一端。我们希望的形式是 $article->user() ，让我们修改 article 模型。

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

在我们的数据库中，文章模型没有用户的外键，我们需要设置，修改 create_article_table.php

 Schema::create('articles', function(Blueprint $table)
 {
  $table->increments('id');
      //指定外键列
      $table->integer('user_id')->unsigned();
      $table->string('title');
      $table->text('body');
      $table->timestamp('published_at');
  $table->timestamps();

      //生成外键
      $table->foreign('user_id')
        ->references('id')
        ->on('users')
        ->onDelete('cascade');
 });

因为我们只是在开发阶段，还没有上线运行，我们可以直接修改数据库迁移文件，回滚然后迁移即可，但是如果上线运行的话，应该新建一个迁移。

php artisan migrate:refresh

#输出信息
Rolled back: 2015_03_28_050138_create_article_table
Rolled back: 2014_10_12_100000_create_password_resets_table
Rolled back: 2014_10_12_000000_create_users_table
Nothing to rollback.
Migrated: 2014_10_12_000000_create_users_table
Migrated: 2014_10_12_100000_create_password_resets_table
Migrated: 2015_03_28_050138_create_article_table
Migrated: 2015_03_28_051200_add_excerpt_to_articels_table

现在让我们使用 tinker 来创建一个用户。

php artisan tinker
Psy Shell v0.4.1 (PHP 5.4.16 — cli) by Justin Hileman

#下面是执行过程
>>> $user = new App\User;
=> <App\User #000000007f1ad61a000000006497cc4f> {}
>>> $user->name = &#39;zhang jinglin&#39;;
=> "zhang jinglin"
>>> $user->email = &#39;zjl@example.com&#39;;
=> "zjl@example.com"
>>> $user->password = bcrypt(&#39;pass&#39;);
=> "$2y$10$Nbl2b9wqd.rXqKEsd3pRSOoIyFAFIhbqf71BufwDfS3Guv21SlEx2"
>>> $user->save();
=> true
>>> App\User::first()->toArray();
=> [
    "id"     => "1",
    "name"    => "zhang jinglin",
    "email"   => "zjl@example.com",
    "created_at" => "2015-03-31 03:24:55",
    "updated_at" => "2015-03-31 03:24:55"
  ]
>>>

现在我们需要新发布的文章和用户关联，我们暂时先修改 form_partial.blade.php 来隐藏一个用户id，只是暂时：

复制代码 代码如下:

{{--临时处理--}}
{!! Form::hidden('user_id', 1) !!}

同时要修改模型的 $fillabel 属性，以便我们的 Mass Assisment。

 protected $fillable = [
    'title',
    'body',
    'published_at',
    'user_id' //临时设置
  ];

OK，添加一个文章。我们使用 tinker 来查看一下。

php artisan tinker
Psy Shell v0.4.1 (PHP 5.4.16 — cli) by Justin Hileman
>>> App\Article::first()->toArray();
=> [
    "id"      => "1",
    "user_id"   => "1",
    "title"    => "User 1 Article",
    "body"     => "User 1 Body",
    "published_at" => "2015-03-31 08:00:00",
    "created_at"  => "2015-03-31 04:17:58",
    "updated_at"  => "2015-03-31 04:17:58",
    "excerpt"   => null
  ]

#获取用户
>>> $user = App\User::first();
=> <App\User #0000000051cbb9d70000000073e11a3e> {
    id: "1",
    name: "zhang jinglin",
    email: "zjl@example.com",
    created_at: "2015-03-31 03:24:55",
    updated_at: "2015-03-31 03:24:55"
  }

#获取用户文章
>>> $user->articles()->toArray();
BadMethodCallException with message &#39;Call to undefined method Illuminate\Database\Query\Builder::toArray()&#39;
>>> $user->articles->toArray();
=> [
    [
      "id"      => "1",
      "user_id"   => "1",
      "title"    => "User 1 Article",
      "body"     => "User 1 Body",
      "published_at" => "2015-03-31 08:00:00",
      "created_at"  => "2015-03-31 04:17:58",
      "updated_at"  => "2015-03-31 04:17:58",
      "excerpt"   => null
    ]
  ]
  
#为什么使用 $user->articles 而不是 #user->articles()?
#事实上，$user->articles()返回的是关系，如果你想用 articles() 你需要这样用
>>> $user->articles()->get()->toArray();
=> [
    [
      "id"      => "1",
      "user_id"   => "1",
      "title"    => "User 1 Article",
      "body"     => "User 1 Body",
      "published_at" => "2015-03-31 08:00:00",
      "created_at"  => "2015-03-31 04:17:58",
      "updated_at"  => "2015-03-31 04:17:58",
      "excerpt"   => null
    ]
  ]
  
#你只能使用 articles() 来进行下一步的工作，比如下面的查询

$user->articles()->where(&#39;title&#39;, &#39;User 1 Article&#39;)->get();

#我们也可以通过 article 获取 user

>>> $article = App\Article::first();
=> <App\Article #0000000051cbb9d60000000073e11a3e> {
    id: "1",
    user_id: "1",
    title: "User 1 Article",
    body: "User 1 Body",
    published_at: "2015-03-31 08:00:00",
    created_at: "2015-03-31 04:17:58",
    updated_at: "2015-03-31 04:17:58",
    excerpt: null
  }
>>> $article->user;
=> <App\User #0000000051cbb92d0000000073e11a3e> {
    id: "1",
    name: "zhang jinglin",
    email: "zjl@example.com",
    created_at: "2015-03-31 03:24:55",
    updated_at: "2015-03-31 03:24:55"
  }
>>>

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