Laravel 5 基础（十一）- Eloquent 关系

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 = 'zhang jinglin';
=> "zhang jinglin"
>>> $user->email = 'zjl@example.com';
=> "zjl@example.com"
>>> $user->password = bcrypt('pass');
=> "$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：

{{--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 'Call to undefined method Illuminate\Database\Query\Builder::toArray()'
>>> $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('title', 'User 1 Article')->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"
   }
>>>