The code below shows how to enhance a base model from a custom query.

<?php
 
/**
 * Subclass for representing a row from the 'md_components' table.
 *
 *
 *
 * @package lib.model
 */
class Navigation extends BaseNavigation
{
 
    private $customAttributes = array(
            "isLevel", 
            "selfFirstLevel", 
            "hasChilds", 
            "prevSibling", 
            "nextSibling", 
            "firstChild", 
            "lastChild", 
            "prevRoot", 
            "nextRoot", 
            "selfRoot"
            );
 
    protected function getCustomAttributes(){
        return $this->customAttributes();
    }
 
    public function makeNextRoot()
    {
        $max = $this->getMaxRight();
        $this->setLeftValue($max + 1);
        $this->setRightValue($max + 2);
    }
 
    public function getNavigationId(){
        return $this->getComponentId();
    }
 
    public function getMaxRight(){
 
        $connection = Propel::getConnection();
        $query = 'SELECT MAX(%s) AS max FROM %s';
 
        $query = sprintf($query, NavigationPeer::TREE_RIGHT, NavigationPeer::TABLE_NAME);
        $statement = $connection->prepareStatement($query);
        $resultset = $statement->executeQuery();
        $resultset->next();
        return $resultset->getInt('max');
    }
 
    public function getMaxLeft(){
        $connection = Propel::getConnection();
        $query = 'SELECT MAX(%s) AS max FROM %s';
        $query = sprintf($query, NavigationPeer::TREE_LEFT, NavigationPeer::TABLE_NAME);
        $statement = $connection->prepareStatement($query);
        $resultset = $statement->executeQuery();
        $resultset->next();
        return $resultset->getInt('max');
    }
 
    public function getRootNodes(){
 
        $connection = Propel::getConnection();
        $query = 'SELECT * FROM %s WHERE %s %s %s;';
 
        $query = sprintf($query, NavigationPeer::TABLE_NAME, NavigationPeer::TREE_PARENT, Criteria::EQUAL, 0);
        $statement = $connection->prepareStatement($query);
        $resultset = $statement->executeQuery();
        $credential = array();
        foreach($resultset as $result){
            $credential[$result["name"]]["component_id"] = $result["component_id"];
            $credential[$result["name"]]["name"] = $result["name"];
            $credential[$result["name"]]["left"] = $result["tree_left"];
            $credential[$result["name"]]["right"] = $result["tree_right"];
        }
        return $credential;
    }
 
 
    public function getTree($offset = 0, $limit = 10, $options = null){
 
 
        $query = '
SELECT
    *,
    (
        SELECT
            CONCAT(COUNT(*))
        FROM md_components MA
        WHERE
        (
            (
                MA.TREE_LEFT < MM.TREE_LEFT AND MA.TREE_RIGHT > MM.TREE_RIGHT
            )
            AND MA.TREE_SCOPE = MM.TREE_SCOPE
        )
    )
    AS isLevel,
    (
        SELECT MZ4.COMPONENT_ID
                FROM md_components MZ4 , md_components MZ5
                WHERE MZ5.TREE_LEFT BETWEEN MZ4.TREE_LEFT AND MZ4.TREE_RIGHT
                AND MZ5.COMPONENT_ID = MM.COMPONENT_ID
                ORDER BY MZ4.TREE_LEFT  LIMIT 1,1
    )
    AS selfFirstLevel,
    (
        SELECT
            IF( MB.TREE_RIGHT - MB.TREE_LEFT > 1, 1, 0)
        FROM md_components MB
        WHERE MB.COMPONENT_ID = MM.COMPONENT_ID
        AND MB.TREE_SCOPE = MM.TREE_SCOPE
    )
    AS hasChilds,
    (
        SELECT MC.COMPONENT_ID FROM md_components MC
        WHERE (MM.TREE_LEFT = MC.TREE_RIGHT + 1)
        AND MC.TREE_SCOPE = MM.TREE_SCOPE
    )
    AS prevSibling,
    (
        SELECT
            MD.COMPONENT_ID
        FROM md_components MD
        WHERE (MM.TREE_RIGHT = MD.TREE_LEFT - 1)
        AND MD.TREE_SCOPE = MM.TREE_SCOPE
    )
    AS nextSibling,
    (
        SELECT
            IF
            (
                (
                    SELECT
                        IF
                        (
                            MQ.TREE_RIGHT - MQ.TREE_LEFT > 1,
                            1,
                            0
                        )
                    FROM md_components MQ
                    WHERE MQ.COMPONENT_ID = MM.COMPONENT_ID
                    AND MQ.TREE_SCOPE = MM.TREE_SCOPE
                ) = 1 ,
                ME.COMPONENT_ID,
                NULL
            )
        FROM md_components ME
        WHERE ME.TREE_LEFT = MM.TREE_LEFT + 1
        AND ME.TREE_SCOPE = MM.TREE_SCOPE
    )
    AS firstChild,
    (
        SELECT
            IF
            (
                (
                    SELECT
                        IF(
                            MS.TREE_RIGHT - MS.TREE_LEFT > 1,
                            1,
                            0
                        )
                    FROM md_components MS
                    WHERE MS.COMPONENT_ID = MM.COMPONENT_ID
                    AND MS.TREE_SCOPE = MM.TREE_SCOPE
                ) = 1 ,
                MF.COMPONENT_ID,
                NULL
            )
        FROM md_components MF
        WHERE MF.TREE_RIGHT = MM.TREE_RIGHT - 1
        AND MF.TREE_SCOPE = MM.TREE_SCOPE
 
    )
    AS lastChild,
    (
              SELECT
            MX.COMPONENT_ID
            FROM md_components MX
        WHERE MX.TREE_LEFT - 1 =
        (
                  SELECT
            MZ.TREE_RIGHT
            FROM md_components MZ
            WHERE (MZ.TREE_RIGHT > MM.TREE_RIGHT) AND (MZ.TREE_LEFT < MM.TREE_LEFT) AND (MZ.TREE_PARENT = 0)
            AND MZ.TREE_SCOPE = MM.TREE_SCOPE
        )
 
    )
    AS nextRoot,
    (
        SELECT
            MX.COMPONENT_ID
            FROM md_components MX
        WHERE MX.TREE_RIGHT + 1 =
        (
                  SELECT
            MZ2.TREE_LEFT
            FROM md_components MZ2
            WHERE (MZ2.TREE_RIGHT > MM.TREE_RIGHT) AND (MZ2.TREE_LEFT < MM.TREE_LEFT) AND (MZ2.TREE_PARENT = 0)
            AND MZ2.TREE_SCOPE = MM.TREE_SCOPE
        )
 
    )
    AS prevRoot,
    (
            SELECT
            MZ3.COMPONENT_ID
            FROM md_components MZ3
            WHERE (MZ3.TREE_RIGHT > MM.TREE_RIGHT) AND (MZ3.TREE_LEFT < MM.TREE_LEFT) AND (MZ3.TREE_PARENT = 0)
            AND MZ3.TREE_SCOPE = MM.TREE_SCOPE
 
    )
    AS selfRoot
 
FROM md_components MM
';
 
        $query .= ' ORDER BY MM.TREE_LEFT ASC ';
        $query .= 'LIMIT '. $offset . ', ' . $limit;
 
        $connection = Propel::getConnection();
        $statement = $connection->createStatement(  );
        $result = $statement->executeQuery( $query , ResultSet::FETCHMODE_NUM);
 
        $objects = NavigationPeer::populateObjects( $result );
 
        $phpNames = NavigationPeer::getFieldNames(BasePeer::TYPE_PHPNAME);
 
        // merge custom and native attributes
        $additionalColumns = array_merge( $phpNames, $this->getCustomAttributes() );
 
        foreach($result as $key => $object){
            foreach($object as $column => $value){
                if($column > count($phpNames)-1){
                    $method = $additionalColumns[$column];
                    $objects[$key-1]->$method = $value;
                }
            }
        }
        return $objects;
    }
 
    /*custom getter functions*/
    public function lastChild(){
        return $this->lastChild;
    }
 
    public function selfFirstLevel(){
        return $this->selfFirstLevel;
    }
 
    public function firstChild(){
        return $this->firstChild;
    }
 
    public function prevRoot(){
        return $this->prevRoot;
    }
 
    public function nextRoot(){
        return $this->nextRoot;
    }
 
    public function selfRoot(){
        return $this->selfRoot;
    }
 
    public function nextSibling(){
        return $this->nextSibling;
    }
 
    public function prevSibling(){
        return $this->prevSibling;
    }
 
    public function isLevel(){
        return $this->isLevel;
    }
 
    public function hasChilds(){
        return $this->hasChilds;
    }
}
 
$columns_map = array
(
    'left'   => NavigationPeer::TREE_LEFT,
    'right'  => NavigationPeer::TREE_RIGHT,
    'parent' => NavigationPeer::TREE_PARENT,
    'scope'  => NavigationPeer::TREE_SCOPE
);
 
sfPropelBehavior::add('Navigation', array('actasnestedset' => array('columns' => $columns_map)));