Best way to handle dirty state in an ORM model

_{Attention!
My opinion on the subject has somewhat changed in the past month. While the answer where is still valid, when dealing with large object graphs, I would recommend using Unit-of-Work pattern instead. You can find a brief explanation of it in this answer}

I’m kinda confused how what-you-call-Model is related to ORM. It’s kinda confusing. Especially since in MVC the Model is a layer (at least, thats how I understand it, and your “Models” seem to be more like Domain Objects).

I will assume that what you have is a code that looks like this:

  $model = new SomeModel;
  $mapper = $ormFactory->build('something');

  $model->setId( 1337 );
  $mapper->pull( $model );

  $model->setPayload('cogito ergo sum');

  $mapper->push( $model );

And, i will assume that what-you-call-Model has two methods, designer to be used by data mappers: getParameters() and setParameters(). And that you call isDirty() before mapper stores what-you-call-Model‘s state and call cleanState() – when mapper pull data into what-you-call-Model.

_{BTW, if you have a better suggestion for getting values from-and-to data mappers instead of setParameters() and getParameters(), please share, because I have been struggling to come up with something better. This seems to me like encapsulation leak.}

This would make the data mapper methods look like:

  public function pull( Parametrized $object )
  {
      if ( !$object->isDirty() )
      {
          // there were NO conditions set on clean object
          // or the values have not changed since last pull
          return false; // or maybe throw exception
      }

      $data = // do stuff which read information from storage

      $object->setParameters( $data );
      $object->cleanState();

      return $true; // or leave out ,if alternative as exception
  }

  public static function push( Parametrized $object )
  {
      if ( !$object->isDirty() )
      {
          // there is nothing to save, go away
          return false; // or maybe throw exception
      }

      $data = $object->getParameters();
      // save values in storage
      $object->cleanState();

      return $true; // or leave out ,if alternative as exception
  }

_{In the code snippet Parametrized is a name of interface, which object should be implementing. In this case the methods getParameters() and setParameters(). And it has such a strange name, because in OOP, the implements word means has-abilities-of , while the extends means is-a.}

Up to this part you should already have everything similar…

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Now here is what the isDirty() and cleanState() methods should do:

  public function cleanState()
  {
      $this->is_dirty = false;
      $temp = get_object_vars($this);
      unset( $temp['variableChecksum'] );
      // checksum should not be part of itself
      $this->variableChecksum = md5( serialize( $temp ) );
  }

  public function isDirty()
  {
      if ( $this->is_dirty === true )
      {
          return true;
      }

      $previous = $this->variableChecksum;

      $temp = get_object_vars($this);
      unset( $temp['variableChecksum'] );
      // checksum should not be part of itself
      $this->variableChecksum = md5( serialize( $temp ) );

      return $previous !== $this->variableChecksum;
  }