laravel 多对多 belonsToMany

1. 建库，建model

   php artisan make:migration create_tags_table --create=tags
   php artisan make:model Tag

2. 加字段

   <?php
   
   use IlluminateDatabaseSchemaBlueprint;
   use IlluminateDatabaseMigrationsMigration;
   
   class CreateTagsTable extends Migration
   {
   
       public function up()
       {
           Schema::create('tags', function (Blueprint $table) {
               $table->increments('id');
               $table->string('name');
               $table->timestamps();
           });
   　　　　　　//字母顺序，单数形式表名下划线结合定义中间表名
           Schema::create('article_tag', function (Blueprint $table) {
               $table->integer('tag_id')->unsigned()->index();
               $table->foreign('tag_id')->references('id')->on('tags')->onDelete('cascade');
               $table->integer('article_id')->unsigned()->index();
               $table->foreign('article_id')->references('id')->on('articles')->onDelete('cascade');
               $table->timestamps();
           });
       }
   
       public function down()
       {
           Schema::drop('tags');
           Schema::drop('article_tag');
       }
   }

3. 添加关系

   //在Article模型中
       public function tags()
       {
           return $this->belongsToMany('AppTag');
       }
   //在Tag中
       public function articles()
       {
           return $this->belongsToMany('AppArticle');
       }

4. 调用

   $article->tags()->attach($id)
   $tag->articles()->attach($id)

5. 视图多选框

       <div class='form-group'>    
           {!! Form::label('tags', 'Tags') !!}
           {!! Form::select('tags[]',$tags, null, ['class'=>'form-control','multiple']) !!}
       </div>    

6. create ,  store

       public function create()
       {
           $tags = AppTag::lists('name','id');
   
           return view('articles.create', compact('tags'));
       }
   
       public function store(ArticleRequest $request)
       {
           
           $article = Auth::user()->articles()->create($request->all());
   
           $article->tags()->attach($request->tags);
   
           flash()->success('Your article has been created!');
   
           return  redirect('articles');
   
       }