PHP mongodb AR

<?php
/**
 * @author xiaojiang
 */
abstract class MongoAr{

    private $db = null;

    public function __construct(){
        $this->db = $this->getCol();
    }

    protected function rules(){
        return array();
    }

    //获取写链接
    public function getW(){
        return $this->db->w();
    }
    //获取读链接
    public function getR(){
        return $this->db->r();
    }

    public function checkRule( $w ){

        $rules = $this->rules();
        if( !$rules )
            return $w;
        foreach( $w as $k => &$v ){
            foreach ( $this->rules() as $r ){
                if(  strpos( $r[0], $k ) !== false ){
                     $v = $this->setType( $v ,$r[1] );
                }
            }
        }
        return $w;
    }

    /**
     * change type by use of force.
     * @param unknown $v
     * @param unknown $type
     */
    public function setType( $v, $type ){
        switch ( $type ){
            case 'int':
                $v = (int)$v;
                break;
            case 'object_id':
                $v = new MongoId($v);
                break;
            case 'string':
            default:
                $v = (string)$v;
                break;
        }
        return $v;
    }

    public function find( $where, $option = array() ){
        $where = $this->checkRule( $where );
        $_fields = array();
        if( !empty( $option['fields'] ) ){
            $_fields = explode(',', $option['fields']);
        }
        $cursor = $this->db->r()->selectDb( $this->getDbName() )->selectCollection( $this->getColName() )->find( $where ,$_fields );

        if( !empty( $option['sort'] ) ){
            $cursor = $cursor->sort( $option['sort'] );
        }
        if( !empty( $option['page'] ) ){
            $option['offset'] = ( $option['page'] -1 ) * $option['page_size'];
            $option['limit'] = $option['page_size'];
        }
        if( !empty( $option['limit'] ) ){
            if( !empty( $option['offset'] ) ){
                $cursor = $cursor->skip( $option['offset'] );
            }
            $cursor = $cursor->limit( (int)$option['limit'] );
        }
        return iterator_to_array( $cursor );
    }

    public function findOne( $where ){
        $where = $this->checkRule( $where );
        $_fields = array();
        if( !empty( $option['fields'] ) ){
            $_fields = explode(',', $option['fields']);
        }
        return $this->db->r()->selectDb( $this->getDbName() )->selectCollection( $this->getColName() )->findOne( $where, $_fields );
    }

    public function insert( $data, $opt ){
        return $this->db->w()->selectDb( $this->getDbName() )->selectCollection( $this->getColName() )->insert( $data, $opt );
    }

    public function update( $where, $data ,$opt = array() ){
        $ret = $this->db->w()->selectDb( $this->getDbName() )->selectCollection( $this->getColName() )->update( $where, $data, $opt );
        return $ret;
    }
}

?>

MongoAr.php

<?php
/**
 * @author jiangzaixing
 */
class MongoModel extends MongoAr{

    public $pk = '_id';
    private $attributes = array();
    protected $mongodb_col = null;
    static $models = array();
    static public function getInstance( $name = __CLASS__ ){
        if( !isset(self::$models[$name]) )
            self::$models[$name] = new $name();
        return self::$models[$name];
    }

    /**
     * 获取当前collection
     */
    protected function getCol(){}

    /**
     * get table name
     */
    protected function getColName(){}

    public function setAttributes( array $arr ){
        $this->attributes = $arr;
        return $this;
    }

    public function save(){

        $pValue = ( isset( $this->attributes[$this->pk] ) && !empty( $this->attributes[$this->pk] ) ) ? $this->attributes[$this->pk] : '';
        if( empty( $pValue ) ){
            $ret = $this->insert( $this->attributes );
        }else{
            $this->attributes = $this->checkRule( $this->attributes );
            $where[$this->pk] = $this->attributes[$this->pk];
            unset( $this->attributes[$this->pk] );
            $ret = $this->update( $where , array('$set'=>$this->attributes ) );
        }
        return $ret;
    }

}

?>

MongoModel.php