表联接跨PHP和MySQL中的多个数据库表和对象

Question

I have 4 classes, each with their own database tables:

• GlobalObject
• Image
• Project
• Page

GlobalObject has 3 properties

• global_object_id
• added_by
• datetime_added

Image, Project and Page have many different fields, they ALL have the following though:

• id
• global_object_id (Foreign key)

At the moment, my class structure has Images, Projects and Pages as subclasses of the GlobalObject class, this allows the 3 subclasses access to the variables that are required of them, datetime_added etc.

How should I set the properties using PHP and MySQL? At the moment, ALL of the fields (including those in the global_object table) are in each section's table (except global_object_id which cannot exist without the new table - and is why I need to do this), So i request the data from the Image table for example, which includes all the properties in the parent class and is set using parent::set_by_row($database_args), and $this->set_by_row($database_args);

At the moment I do the following (Using Image as an example):

class Image extends GlobalObject
{
$id;
$title;

function set_by_id($id)
{
// Select Q from Image table
$this->set_by_row($db_result);
}

function set_by_row($args)
{
parent::set_by_row($args);
// Set class properties
}

}

To reiterate: I want to be able to do the following:

$image = new Image()
$image->set_by_global_object_id(23);

And the image be set, including everything in the parent class (which is stored in a separate table)

Please ask away if any of that is unclear.

Answer 1

A very convenient way is offered by those "magic methods", like __get and __set. The following example provides read-only access to the data, but can easily be extended with a __set method.

abstract class GlobalObject {
    protected $_data = array();

    /* Magic Method: Enable read access via $this->name */
    public function __get($key) {
        if (isset($this->_data[$key])) {
            return $this->_data[$key];
        }
        throw new Exception('Property "'. $key .'" not found.');
    }

    protected function _setFromArray(array $data) {
        // .. do whatever needs to be done with the data ..

        $this->_data = $data;
    }
}

Now just extend this class:

class Image extends GlobalObject {
    public function setByGlobalId($id) {
        $result = mysql_query('SELECT i.*, g.* FROM images AS i
            LEFT JOIN global_objects AS g
            ON g.global_object_id = i.global_object_id 
            WHERE i.global_object_id = '. intval($id) .' LIMIT 1');

        // @todo check if result is empty

        $data = mysql_fetch_assoc($result);
        $this->_setFromArray($data);
    }
}

And a simple example:

$image = new Image();
$image->SetByGlobalId(42);
echo $image->added_by;