cssd-back/app/MedicalCenter.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class MedicalCenter extends Model
{
    public $fillable = ['name', 'city_id', 'address', 'phone_number'];

    public function users()
    {
        return $this->hasMany('App\User');
    }

    public function city()
    {
        return $this->belongsTo('App\City');
    }
}