PHP return self as array of objects from within the class?

Question

I'm using CodeIgniter to build a php web application, and I'm trying to use good OO practices - of which there appears to be many schools of thought. I specifically have a class biography_model to interact with a MySQL table. This data model has some class properties representing the columns in the table, but it also has some properties not in the table such as $image_url. The class constructor function accepts an optional record ID parameter which then fetches that record from the table and sets all object properties by calling the get_biography() method, including the $image_url property not in the table. This way I can instantiate a new biography_model object in the controller with all useful properties ready to go: $bio = new biography_model($id);

But, what is the best approach when we are returning a multi-row result set of records from the table? For each record I need to also set the $image_url. I could do this in the controller, by querying the list of records in the table and then passing each id into the new biography_model($id) object. But then I would have a situation where the controller is directly querying the database bypassing the model.

Instead, I choose to return an array of biography_model objects from within the biography_model.

Example:

    class Biography_model extends Model
    {
        /**
         *  This model manages biography information in the 'biography_content' table.
         *  If a biography ID is passed in when instantiating a new object,
         *  then all class properties are set.
         */
        protected $id;
        protected $person_name;
        protected $title;
        protected $image_file_name;
        protected $image_url;
        protected $biography_text;
        protected $active;

        /**
         * Constructor
         *
         *  If an id is supplied when instantiating a new object, then
         *  all class variables are set for the record.
         */
        public function __construct($person_id = NULL)
        {
            parent::Model();
            if(isset($person_id))
            {
                $this->set_property('id',$person_id);
                $this->get_biography();
            }
        }

        /**
         * Sets supplied property with supplied value.
         */
        public function set_property($property, $value)
        {
            // Set image path if $value is the file name
            if($property == 'image_file_name')
            {
                $this->set_property('image_url',$this->get_bio_img_url($value));
            }

            $this->$property = $value;
        }

        /**
         * Gets requested property value.
         */
        public function get_property($property)
        {
            return $this->$property;
        }

        /**
         *  Returns the biography thumbnail image URL
         */
        public function get_bio_img_url($image_name)
        {
            return $this->config->item('parent_url').'assets/img/biography/'.$image_name;
        }

        /**
         * Get one or more biography entries
         */
        public function get_biography()
        {
            // If the ID is set then set model properties.
            if($this->get_property('id'))
            {
                $this->db->where('id',$this->get_property('id'));
                $query = $this->db->get('biography_content');

                if($query->num_rows() == 1)
                {
                    foreach($query->row() as $key => $value)
                    {
                        $this->set_property($key, $value);
                    }
                }
            }
            // Otherwise return result set of all biographies
            else
            {
                // Get the list of record ID's
                $this->db->select('id');
                $query = $this->db->get('biography_content');

                if ($query->num_rows() > 0)
                {   
                    // New array to return result set
                    $biography_list = array();

                    // For each record, return a new biography_model object
                    foreach($query->result() as $value)
                    {
                        $biography_list[] = new biography_model($value->id);
                    }
                }
                return $biography_list;
            }
        }
    }

    // End of Biography_model Class

It works. But is it a reasonable approach? Are there other more accepted methods? I'm keenly aware that I am querying the database twice, but I was not sure of a better way to handle this. All suggestions are welcome!

Thanks, Wolf

Answer 1

Usually it's better for functions to have one job. Your get_biography() function has 2: get one biography and get all biographies. Consider splitting them up into 2 functions. Also there's no need for the multiple db access.

public function get_biography($id=null)
{
    $this->db->where('id', $this->get_property($id))
    $query = $this->db->get('biography_content');

    foreach($query->row() as $key => $value)
    {
        $this->set_property($key, $value);
    }
}

public function get_biographies()
{
    $biography_list = array();

    // don't limit this query to just id's - get everything
    $query = $this->db->get('biography_content');

    // For each record, return a new biography_model object
    foreach($query->result() as $row)
    {
        $model = new biography_model();
        // set the properties you already have straight onto the new model
        // instead of querying again with just the id
        foreach($row as $key => $value)
        {
            $model->set_property($key, $value);
        }
        $biography_list[] = $model;
    }
    return $biography_list;
}

Also you might want to take advantage of php's __get and __set magic methods:

public function __get($property)
{
    if(!isset($this->$property))
        return null;

    return $this->$property;
}

public function __set($property, $value)
{
    if(!property_exists($this, $property))
        return;

    if($property == 'image_file_name')
    {
        $this->image_url = $this->get_bio_img_url($value);
    }
    else
        $this->$property = $value;
}

This will let you get properties on your model like this: $bio->title instead of $bio->get_property('title') while at the same time provide a place you can introduce new logic later.

Answer 2

Using an array to represent a set of records is a perfectly valid approach.

However the property image_url directly depends on the value of another property, so it doesn't make sense to store it as a separate field. Just calculate it on the fly, in your case you'd have to do that in the get_property method.

On the other hand should the model really be responsible for dealing with URLs? I don't think so. There should be a method outside the model that takes the Biography_model object and generates the URL of the image based on its image_file_name. If you already have some routing module responsible for mapping controllers to URLs, this code should probably land there.