在laravel 5.4中以一种形式添加具有多个表的数据多对多关系

   Schema::create('table1_table2', function (Blueprint $table) {

       $table->unsignedBigInteger('table1_id');

       $table->unsignedBigInteger('table2_id');

       // 可以添加其他字段

       $table->timestamps();

       $table->foreign('table1_id')->references('id')->on('table1')->onDelete('cascade');

       $table->foreign('table2_id')->references('id')->on('table2')->onDelete('cascade');

   });

   return $this->belongsToMany(Table2::class, 'table1_table2', 'table1_id', 'table2_id');

   return $this->belongsToMany(Table1::class, 'table1_table2', 'table2_id', 'table1_id');

 ```php

 $table1 = Table1::find(1);

 $table2 = Table2::find(2);

 $table1->table2()->attach($table2->id);

 ```

 ```php

 $table1 = Table1::find(1);

 $table2s = $table1->table2;

 ```

 ```php

 $table1 = Table1::find(1);

 $table2 = Table2::find(2);

 $table1->table2()->detach($table2->id);

 ```