cssd-back/app/Message.php

<?php

namespace App;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;

class Message extends Model
{
    use SoftDeletes;
    public $fillable = ['title', 'text', 'status', 'recipient_user_id', 'sender_user_id'];
    public function sender_user()
    {
      return $this->belongsTo('App\User', 'sender_user_id');
    }
    public function recipient_user()
    {
      return $this->belongsTo('App\User', 'recipient_user_id');
    }
}