问在Laravel 4中更新枢轴表的附加列

EN

public function up()
    {
        Schema::create('messages', function(Blueprint $table) {
            $table->increments('id');
            $table->mediumText('subject');
            $table->text('message');
            $table->boolean('draft');
            $table->integer('sender_id')->unsigned();
            $table->softDeletes();
            $table->timestamps();

            $table->foreign('sender_id')->references('id')->on('users')->onUpdate('cascade');
        });

        Schema::create('message_assets', function(Blueprint $table) {
            $table->increments('id');
            $table->integer('message_id')->unsigned();
            $table->string('filename', 255);
            $table->softDeletes();

            $table->foreign('message_id')->references('id')->on('messages')->onUpdate('cascade');
        });

        Schema::create('message_users', function(Blueprint $table) {
            $table->increments('id');
            $table->integer('message_id')->unsigned();
            $table->integer('user_id')->unsigned();
            $table->integer('read')->default(0);
            $table->string('folder', 255)->nullable();
            $table->softDeletes();

            $table->foreign('message_id')->references('id')->on('messages')->onUpdate('cascade');
            $table->foreign('user_id')->references('id')->on('users')->onUpdate('cascade');
        });
    }

public function to()
{
    return $this->belongsToMany('SeriousJelly\Modules\Users\Models\User', 'message_users', 'message_id', 'user_id');
}