WP_Model-post-finder.php

<?php
Class Product extends WP_Model
{
    ...
    public function _finderHeavy($agrs){
        ...
    }

    public function _postFinderHeavy($results, $args){
        return array_map(function($model){
            if($model->color == 'blue'){
                return $model;
            }
        }, $results); 
    }
}

$heavyProducts = Product::finder('heavy', ['heavierThan' => 250]); // [Product, Product, Product];
echo $heavyProducts[0]->color; // 'blue'