Question

Can anyone tell me if there is a resolution to saving PHP classes with private members to MongoDb? I keep getting the following error

zero-length keys are not allowed, did you use $ with double quotes?'

I see there at least two existing question pertaining to the same question with no real answers.
Question 1
Question 2

all of my persistence classes have a private member that I need available but I’m not interested in creating a function to avoid the necessity for the private member since this is an instance based class that has multiple function utilizing the private member.

Web server Apache/2.2.22

PHP version PHP 5.4.6

PHP extension mongo/1.2.6

This would be a sample implementation, please don’t critique the code itself it is just to illustrate the type of behavior which is the Save of $this and the $private member in the base type:

<?php

class PersistableObject extends AbstractBasePersistableObject
{
   public  $PublicSubTypeProperty;

    public function __construct()
    {
       parent::__construct();
    }

    public function GetDalConfigurationFromSubType()
    {
        //This object is just a wrapper DAL implemented based on
        //the php Mongo, MongoDb and MongoCollection objects
        return new MongoBasedDal();
    }
}


abstract class AbstractBasePersistableObject
{
   private $dalRef = null;
   public $PublicBaseProperty;

   public abstract function GetDalConfigurationFromSubType();

   public function __construct()
   {
      $this->dalRef = $this->GetDalConfigurationFromSubType();
   }

   public function Save()
   {
       $this->dalRef->Save($this);
   }
}

?>

Answer 1

Can anyone tell me if there is a resolution to saving PHP classes with private members to MongoDb?

The problem, as you know from Google Groups, is that the PHP driver actually omits private and protected variables from save. This is a fundamental problem within the core of the driver itself so there is no easy way around it. As you also know Derick created a JIRA for this: https://jira.mongodb.org/browse/PHP-624

@harald does actually state the way around, to create your own _to_array() and feed that into the save function, unfortunately this derives a fundamental problem again with how you have built your classes. You must use reflection for this like so:

$reflect = new ReflectionClass(get_class($this));
$class_vars = $reflect->getProperties(ReflectionProperty::IS_PUBLIC | ReflectionProperty::IS_PROTECTED | ReflectionProperty::IS_PRIVATE);

foreach ($class_vars as $prop) {
    $doc[$prop->getName()] = $this->{$prop->getName()};
}

And then use $doc within the save.

You can however change your programming a bit to avoid the reflection (or just cache the result of the reflection to save the resource hog) by making a pre-defined array of $schema which will house all the fields you wish to save. When you wish to add new fields on-demand you can just make your __set and __get update the in memory schema array. This way you can avoid the reflection altogether and just go for grabbing the schema array and it’s values.

This is the method a lot of frameworks use to get around the problem, including Lithium, Yii, Kohona, CakePHP and more.