Table of Contents
1. 创建数据库表
2. 创建模型并指定关系
3. 在Controller中使用
Home Backend Development PHP Tutorial Laravel中的Many-To-Many

Laravel中的Many-To-Many

Jun 23, 2016 pm 01:30 PM

在实际的开发中,我们经常会接触到几种常见的对应关系模式:

One-To-One //一对一One-To-Many //一对多Many-To-Many //多对多
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在刚刚开始接触到这些概念的时候,其实我是不太理解的。但是一旦你将这些概念应用到生活中,理解起来就很简单了,就举一个与我们在网上经常见到的例子:

User-To-Profile // One-To-OneUser-To-Articles // One-To-ManyArticles-To-Tags // Many-To-Many
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翻译过来就是:

  • 一个用户对应一个用户档案
  • 一个用户可以发表多篇文章
  • 而文章和标签确实多对多的关系,一篇文章可以有多个标签;一个标签可以属于多篇文章
  • 在这些关系模型中,最难实现的就是Many-To-Many这种多对多的关系,不过借助Laravel的强大的Eloquent,实现这个功能还是比较顺心的。

    1. 创建数据库表

    创建articles表

    Schema::create('articles', function (Blueprint $table) {            $table->increments('id');            $table->string('title');            $table->text('content');            $table->timestamps();        });
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    创建tags表

    Schema::create('tags', function (Blueprint $table) {            $table->increments('id');            $table->string('name');            $table->timestamps();        });
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    当然,解决这个经典问题单单靠这两张表还不足够,需要在这两张表之外再建立一个关系表,用来将article和tag联系起来,在Laravel中,如果你遵循官方的标准规则,第三张表应该是这样的:

    表名 article_tag

    Schema::create('article_tag', function(Blueprint $table) {            $table->integer('article_id')->unsigned()->index();            $table->foreign('article_id')->references('id')->on('articles')->onDelete('cascade');            $table->integer('tag_id')->unsigned()->index();            $table->foreign('tag_id')->references('id')->on('tags')->onDelete('cascade');        });
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    如果你没有按照官方的规范来,你需要在模型中指定外键。

    2. 创建模型并指定关系

    在Article.php中:

    <br />    public function tags()    {        return $this->belongsToMany('App\Tag');    }
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    在Tag.php中:

    public function articles()    {        return $this->belongsToMany('App\Article');    }
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    这里注意两点:

  • 你可以在声明关系的时候指定外键,如$this->belongsToMany('App\Article','foreign_key', 'other_key');
  • 如果在article_tag表中你添加了timestamps(),即表中出现created_at和updated_at这两个字段,在Article中声明关系的时候需要这样:return $this->belongsToMany('App\Tag')->withTimestamps();
  • 3. 在Controller中使用

    如果我们想查看某个文章含有哪些标签,我们可以这样:

    $article = Article::find($id);dd($article->tags);
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    如果我们想通过某个标签来查找文章:

    <br />public function showArticleByTagName($name)    {        $tag = Tag::where('value','=',$name)->first();        dd($tag->articles);    }
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    以上,就实现了在Laravel中的Many-To-Many.

    Happy Hacking

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