Question

I have multiple objects that I’d like to be accessible via human-readable URLs, so I am generating aliases (e.g. blog.com/this-is-an-alias/) for all database records.

What is the best practice for generating these automatically?

I’m currently hook the model’s ‘values()’ method and producing a new alias in there (based on the required ‘name’ field), but I can’t help but feel this could done more elegantly using, say, Kohana’s built-in filters.

Here’s the stripped-down model:

class Model_Category extends ORM {
    // relevant rules:
    public function rules(){
            return array(
            'alias' => array(
                array('max_length', array(':value', 63)),
                array(array($this, 'unique'), array(':field', ':value')),
            ),
            'name' => array(
                array('max_length', array(':value', 63)),
            ),
            // (...)
        );
    }

    // overrides default method:
    public function values(array $values, array $expected = NULL){
        if(!$this->_loaded){
            if($values['name'] && !$values['alias'])
                $values['alias'] = Helper_Form::to_alias($values['name']);
        }

        return parent::values($values, $expected);
    }
}

FYI, the to_alias function simply looks like this:

return strtolower(substr(trim(preg_replace('/[^0-9a-zA-Z]+/','-',$str),'-'),0,63));

So, my questions:

• is it possible and/or advisable to access a model’s property–other than the one being filtered–from within a filter callback?
  (so far my tests seem to suggest no, or, at best, unreliably)
• more importantly, how can I build-in a uniqueness test? i.e., after auto-generating an alias, how can I be sure that slug isn’t already in use without throwing the model’s rules() exception?

Answer 1

I would do that automatic generation using filters as you mentioned. Below is my conception of doing this. For filter function you can pass some specific parameters like :model, :value, :field and in this case I’d use :model to get access to current model’s properties.

class Model_Category extends ORM {

    public function filters()
    {
        return array(
            'slug' => array(
                array(array($this, 'create_slug'), array(':model')),
            ),
        );
    }

    public function create_slug($model)
    {
        $model = ($model instanceof ORM) ? $model : $this;

        $number = 1;

        $slug = UTF8::transliterate_to_ascii($model->name);
        $slug = preg_replace("/[^a-zA-Z0-9\/_|+ -]/", '', $slug);
        $slug = UTF8::strtolower(trim($slug, '-'));
        $slug = preg_replace("/[\/_|+ -]+/", '-', $slug);

        while ( ! $this->unique_slug($slug))
        {
            if ( ! preg_match('/\d+$/', $slug))
            {
                $slug .= '-'.$number;
            }
            $slug = preg_replace('/\d+$/', $number++, $slug);
        }

        return $slug;
    }

    public function unique_slug($slug)
    {
        return (bool) DB::select(array('COUNT("*")', 'total_count'))
            ->from($this->_table_name)
            ->where('slug', '=', $slug)
            ->where($this->_primary_key, '!=', $this->pk())
            ->execute($this->_db)
            ->get('total_count');
    }

}

Above example may be not fully functional but I hope you get the idea.