baoshi-was/app/City.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class City extends Model
{
    protected $fillable=[
        'province_id','name'
    ];

    protected $appends=[
        'province_name'
    ];

    public  function province(){
        return $this->belongsTo('App\Province','province_id','id');
    }

    public function getProvinceNameAttribute(){
        return $this['province']? $this['province']['name']:null;
    }

}