Learn Laravel5's Eloquent relationship-PHP Tutorial-php.cn

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'); }

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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'); }

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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'); });

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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

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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; =>  {} >>> $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" ] >>>

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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 ];

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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(); =>  { 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(); =>  { 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; =>  { 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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