I found this PHP implementation of 'active record' I did nearly 7 years ago. Below you see an implementation of a model.

active_record.class.php

<?php

class active_record
{
  function table_name()
  {
    return get_class($this);
  }

  function conf($conf=NULL)
  {
    if($conf!==NULL)
    {
      $this->conf=$conf;
    }
    elseif(!isset($this->conf) OR $this->conf==null)
    {
      $this->conf='active_record';
    }
    return $this->conf;
  }
  function __wakeup()
  {
    $this->__CONSTRUCT($this->table_name(),$this->db,$this->conf());
  }

  function __CONSTRUCT($table_name, $db=NULL,$conf=NULL)
  {
    $conf=$this->conf($conf);

    $db=$this->get_db($db);
    global $class_definitions;
    if(!isset($class_definitions[$table_name]) OR count($class_definitions[$table_name])==0)
    {
      $query='DESCRIBE '.$db->real_escape_string($GLOBALS['config']->$conf->table_prefix.$table_name);
      $result=$db->query($query);
      while($row=$db->fetch_assoc($result))
      {
        $field=$row['Field'];
        $GLOBALS['class_definitions'][$table_name][$field]=$row['Default'];
        if(!isset($this->$field))
        {
          $default=$row['Default'];
          eval("\$this->$field='$default';");
        }
      }
      unset($result);
    }
  }
  function load($identification=NULL, $identification_field=NULL, $recursive=FALSE, $db=NULL, $search=NULL)
  {
    global $class_definitions;
    $db=$this->get_db($db);
    $conf=$this->conf();
    if($identification===NULL AND $identification_field===NULL)
    {
      $identification_string='';
    }
    else
    {
      $identification_string=$this->get_identification_string($identification, $identification_field, $db, $search);
    }
    $query='SELECT * FROM '.$GLOBALS['config']->$conf->table_prefix.$this->table_name().$identification_string;
    $result=$db->query($query);
    $classes=array();
    if($db->num_rows($result)>0)
    {

      while($row=$db->fetch_assoc($result))
      {


        if(array_key_exists($this->primary_key_name(), $class_definitions[$this->table_name()]))
        {
          $classes[$row[$this->primary_key_name()]]=$this->assign_vars_from_row($row, NULL, $recursive, $db);
        }
        else
        {
          $classes[]=$this->assign_vars_from_row($row, NULL, $recursive, $db);
        }

      }//Done looping through the returned row
    }//done executing the code for multiple rows
    else
    {//No rows were returned
      $this->generate();
      $classes[]=$this;
    }
    return $classes;
  }//done withthe loading function
  function generate($db=NULL)
  {
    $db=$this->get_db($db);
    global $class_definitions;
    foreach($class_definitions[$this->table_name()] as $field=>$value)
    {
      eval("\$this->$field=\$value;");
    }

  }
  function assign_vars_from_row($row, $class=NULL, $recursive=NULL, $db=NULL)
  {
    $db=$this->get_db($db);
    $conf=$this->conf();
    global $retrieved_classes;
    if($class===NULL)
    {
      $table_name=$this->table_name();
      eval("\$class = new $table_name;");
    }
    foreach($row as $key=>$value)
    {

      if(substr($key, strlen($key)-strlen($GLOBALS['config']->$conf->foreign_key_suffix))==$GLOBALS['config']->$conf->foreign_key_suffix AND $key!=$GLOBALS['config']->$conf->primary_key AND $recursive===TRUE)
      {

        $new_class_name=substr($key, 0, strlen($key)-strlen($GLOBALS['config']->$conf->foreign_key_suffix));
        if(!class_exists($new_class_name))
        {
          $this->new_class($new_class_name, $db);
        }
        if(isset($retrieved_classes[$new_class_name][$value]))
        {
          eval("\$class->$new_class_name".$GLOBALS['config']->$conf->foreign_key_suffix."=\$retrieved_classes['$new_class_name']['$value'];");
        }
        else
        {
          $new_class = new $new_class_name;
          if($GLOBALS['config']->$conf->primary_key_uses_table_name)
          {
            $primary_key=$new_class_name.$GLOBALS['config']->$conf->primary_key;
          }
          else
          {
            $primary_key=$GLOBALS['config']->$conf->primary_key;
          }
          eval("\$new_class->load('$value','".$this->primary_key_name()."', FALSE, \$db);");
          $retrieved_classes[$new_class_name][$value]=$new_class;
          eval("\$class->$key=\$value;");
          eval("\$class->$new_class_name".$GLOBALS['config']->$conf->foreign_key_suffix."=\$new_class;");
        }
      }
      else
      {
        eval("\$class->$key=\"$value\";");
      }
    }
    //$class->load_relatives($db);
    return $class;
  }//Done assigning Vars to Rows

  function new_class($new_class_name, $db=NULL)
  {
    $db=$this->get_db($db);
    if(file_exists($GLOBALS['config']->models_path.$new_class_name.'.class.php') AND !class_exists($new_class_name))
    {
      $snappad->load_model($new_class_name);
    }
    elseif(!class_exists($new_class_name))
    {
        eval("class $new_class_name extends active_record
        {
          function __CONSTRUCT()
          {
            parent::__CONSTRUCT('$new_class_name');
          }
        }
        ");
    }

  }

  function save($recursive=FALSE, $db=NULL)
  {
    $db=$this->get_db($db);
    $conf=$this->conf();
    global $class_definitions;
    $values='';
    if(!isset($class_definitions[$this->table_name()]))
    {
      $this->__CONSTRUCT($this->table_name(),$db);
    }
    foreach($class_definitions[$this->table_name()] as $field=>$default)
    {
      if(array_key_exists($field, $this))
      {
        eval("\$value=\$this->$field;");

        //echo $field.'='.$value.'<br /><br />';
        if(is_object($value))
        {
          //echo 'its an object!';
          if($recursive===TRUE)
          {
            $value->save($recursive, $db);
          }
          $values.=$db->escape_string($field).'="'.$db->escape_string($foreign_key).'", ';
        }
        elseif($field===$this->primary_key_name())
        {
          if($value!=NULL)
          {
            $identification_string ='WHERE '.$db->escape_string($field).'="'.$db->escape_string($value).'"';
            $values.=$db->escape_string($field).'="'.$db->escape_string($value).'", ';
          }
        }
        else
        {
          $values.=$db->escape_string($field).'="'.$db->escape_string($value).'", ';
        }
      }
    }
    $values=trim($values,', ');
    $values.=' ';

    if(isset($identification_string) AND trim($identification_string!=''))
    {
      $query='UPDATE '.$GLOBALS['config']->$conf->table_prefix.$this->table_name().' SET '.$values.$identification_string;
    }
    else
    {
      $query='INSERT INTO '.$GLOBALS['config']->$conf->table_prefix.$this->table_name().' SET '.$values;
    }
    $db->query($query);
    if($db->insert_id()!=0)
    {
      $primary_key_name=$this->primary_key_name();
      eval("\$this->\$primary_key_name=\$db->insert_id();");
    }
  }
  function destroy($identification=NULL, $identification_field=NULL, $db=NULL)
  {
    $db=$this->get_db($db);
    $conf=$this->conf();
    $identification_string=$this->get_identification_string($identification, $identification_field);
    if($identification_string!='')
    {
      $query='DELETE FROM '.$GLOBALS['config']->$conf->table_prefix.$this->table_name().$identification_string;
      $db->query($query);
    }
  }

  function has_one($table, $override_fk=NULL)
  {
    global $class_definitions;
    if($override_fk===NULL)
    {
      $override_fk=$table;
    }
    $this->has_one[$table]=$override_fk;


  }
  function has_many($table, $override_fk=NULL)
  {
    global $class_definitions;
    if($override_fk===NULL)
    {
      $override_fk=$this->table_name();
    }
    $this->has_many[$table]=$override_fk;

  }

  function load_tables($db=NULL)
  {
    $db=$this->get_db($db);
    $conf=$this->conf();
    global $class_definitions;
    $query='SHOW TABLES';
    $result=$db->query($query);
    while($row=$db->fetch_array($result))
    {
      if(!isset($class_definitions[substr($row[0],strlen($GLOBALS['config']->$conf->table_prefix))]))
      {
        $class_definitions[substr($row[0],strlen($GLOBALS['config']->$conf->table_prefix))]='';
      }
    }
  }

  function load_relatives($db=NULL)
  {
    $db=$this->get_db($db);
    $conf=$this->conf();
    if(isset($this->has_one))
    {
      foreach($this->has_one as $table=>$join_fk)
      {
        if(!class_exists($table))
        {
          $this->new_class($table);
        }
        $temp_class=new $table;

        eval("\$value=\$this->$join_fk".$GLOBALS['config']->$conf->foreign_key_suffix.";");
        $temp_class=$temp_class->load($value, $this->primary_key_name(), FALSE, $db);
        eval("\$this->$table=\$temp_class;");
      }
    }
    if(isset($this->has_many))
    {
      foreach($this->has_many as $table=>$join_fk)
      {
        if(!class_exists($table))
        {
          $this->new_class($table, $db);
        }
        $temp_class=new $table;
        if($GLOBALS['config']->$conf->primary_key_uses_table_name)
        {
          $primary_key=$this->table_name().$GLOBALS['config']->$conf->primary_key;
        }
        else
        {
          $primary_key=$GLOBALS['config']->$conf->primary_key;
        }
        eval("\$value=\$this->$primary_key;");
        $temp_class=$temp_class->load($value, $join_fk.$GLOBALS['config']->$conf->foreign_key_suffix, FALSE, $db);
        eval("\$this->$table=\$temp_class;");
      }

    }
  }
  function get_identification_string($identification=NULL, $identification_field=NULL, $db=NULL, $search=NULL)
  {
    $db=$this->get_db($db);
    $identification_string=' WHERE ';
    if(is_array($identification) AND count($identification)>0)
    {
      foreach($identification as $ident_field=>$ident_val)
      {
        $identification_string.=$db->escape_string($ident_field);
        if(isset($identification_field[$ident_field]))
        {
          if($identification_field[$ident_field]=='like')
          {
            $identification_string.=' LIKE "%'.$db->escape_string($ident_val).'%" AND ';
          }
          else
          {
            $identification_string.=$identification_field[$ident_field].' "'.$db->escape_string($ident_val).'" AND ';
          }
        }
        elseif($search===NULL)
        {
          $identification_string.='="'.$db->escape_string($ident_val).'" AND ';
        }
        else
        {
          $identification_string.=' LIKE "%'.$db->escape_string($ident_val).'%" AND ';
        }
      }
      $identification_string = rtrim($identification_string, ' AND');
    }
    else
    {
      if($identification===NULL)
      {
        eval("\$identification=\$this->".$this->primary_key_name().";");
      }

      if($identification_field==NULL)
      {
        $identification_field=$this->primary_key_name();
      }
      if($search===NULL)
      {
        $identification_string.=$db->escape_string($identification_field).'="'.$db->escape_string($identification).'"';
      }
      else
      {
        $identification_string.=$db->escape_string($identification_field).' LIKE "%'.$db->escape_string($identification).'%"';
      }
    }
    if($identification_string!=' WHERE')
    {
      return $identification_string;
    }
  }

  function primary_key_name($table=NULL)
  {
    $conf=$this->conf();
    if($table===NULL)
    {
      $table=$this->table_name();
    }
    if(isset($this->primary_key_name))
    {
      $primary_key_name=$this->primary_key_name;
    }
    elseif($GLOBALS['config']->$conf->primary_key_uses_table_name)
    {
      $primary_key_name=$table.$GLOBALS['config']->$conf->primary_key;
    }
    else
    {
      $primary_key_name=$GLOBALS['config']->$conf->primary_key;
    }

    return $primary_key_name;
  }

  function is_unique($identification=NULL, $identification_field=NULL, $db=NULL)
  {
    $db=$this->get_db($db);
    $query='SELECT * FROM '.$this->table_name().$this->get_identification_string($identification,$identification_field, $db);
    $result = $db->query($query);
    if($db->num_rows($result)>0)
    {
      return false;
    }
    else
    {
      return true;
    }
  }
  function get_db($db=NULL)
  {
    if($db!==NULL AND is_object($db) AND $db->link!=NULL)
    {
      $this->db=&$db;
    }
    if(!isset($this->db) OR $this->db->link()==NULL)
    {
      $this->db=&$GLOBALS['db'];
    }
    return $this->db;
  }

  function search($identification=NULL, $identification_field=NULL, $db=NULL)
  {
    $db=$this->get_db($db);
    $query='SELECT * FROM '.$this->table_name().$this->get_identification_string($identification,$identification_field,$db,TRUE);
  }
}

?>

event.php

<?
$GLOBALS['snappad']->load_module('active_record');

class event extends active_record
{
  function __CONSTRUCT()
  {
    parent::__CONSTRUCT('event',$GLOBALS['db']);
  }

  function load($identification=NULL, $identification_field=NULL, $recursive=FALSE, $db=NULL, $search=NULL)
  {
    $events = parent::load($identification,$identification_field,$recursive,$db,$search);
    foreach($events as &$event)
    {
      if(isset($event->id))
      {
        $event->load_usage_dates();
        $event->load_venues();
      }
    }
    return $events;

  }

  function destroy($identification=NULL, $identification_field=NULL, $db=NULL)
  {
    $GLOBALS['snappad']->load_model('event_date');
    $GLOBALS['snappad']->load_model('event_venue_link');
    if($identification===NULL AND $identification_field===NULL)
    {
      $event_date = new event_date;
      $event_date->destroy($this->id,'event_id');
      $event_venue_links = new event_venue_link;
      $event_venue_links->destroy($this->id,'event_id');
    }
    parent::destroy($identification,$identification_field,$db);
  }


  function load_usage_dates()
  {
    $GLOBALS['snappad']->load_model('event_date');
    $usage_dates = new event_date;
    $this->usage_dates = $usage_dates->load($this->id,'event_id');
    if(isset($this->usage_dates))
    {
      return true;
    }
    else
    {
      return false;
    }
  }

  function load_venues()
  {
    $GLOBALS['snappad']->load_model('event_venue_link');
    $GLOBALS['snappad']->load_model('venue');
    $event_venue_links = new event_venue_link;
    $event_venue_links = $event_venue_links->load($this->id,'event_id');
    foreach($event_venue_links as $event_venue_link)
    {
      $venue = new venue;
      $venue = current($venue->load($event_venue_link->venue_id,'id'));
      $this->venues[$venue->id]=$venue;
    }
    if(isset($this->venues))
    {
      return true;
    }
    else
    {
      return false;
    }
  }
}

?>