Laravel中的Many-To-Many
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
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
翻译过来就是:
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(); });
创建tags表
Schema::create('tags', function (Blueprint $table) { $table->increments('id'); $table->string('name'); $table->timestamps(); });
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'); });
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'); }
在Tag.php中:
public function articles() { return $this->belongsToMany('App\Article'); }
这里注意两点:
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($article->tags);
如果我们想通过某个标签来查找文章:
<br />public function showArticleByTagName($name) { $tag = Tag::where('value','=',$name)->first(); dd($tag->articles); }
以上,就实现了在Laravel中的Many-To-Many.
Happy Hacking

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