Thoughts @ Dotner

After using Django and it’s hibernate-like Object-Relational Model (ORM) for a month or so, I decided to try how I could create a similar model mechanism using PHP. Here’s an example which I wanted to keep just under 100 lines for light reading. This example code demonstrates how to:

• Easily create a structure with various types of fields (though currently it only supports CharField)
• Generate SQL code for table creation
• Generate a HTML form for editing the information

When you run the example, it will output the following (note the intentional error in the SQL statement syntax):

CREATE TABLE `person` (
`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
`name` VARCHAR(40),
`address` VARCHAR(40),
`phone` VARCHAR(15),
);

<form action=’.’ method=’POST’>
<table>
<tr><th>Name</th><td></td></tr>
<tr><th>Address</th><td></td></tr>
<tr><th>Phone</th><td></td></tr>
</table>
</form>

The code itself is here for you to use in any way you please, as long as you don’t hold me accountable for the results:

download code
run code

<?php

class Field
{
    var $size;
    var $label;
    var $editor;
    var $value;

    function __construct($size = 80, $label = '')
    {
        $this->size = $size;
        $this->label = $label;
    }
}

class CharField extends Field
{
    function __construct($size = 80, $label = '')
    {
        $this->editor = 'input type="text"';
        parent::__construct($size, $label);
    }

    function get_db_type()
    {
        return 'VARCHAR('.$this->size.')';
    }
}

class Model
{
    function get_name()
    {
        return get_class($this);
    }

    function make_create_sql()
    {
        $str = '';
        echo "nCREATE TABLE `",strtolower($this->get_name()),"` (n";
        echo "   `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,n";

        foreach ( get_class_vars($this->get_name()) as $x => $y)
        {
            echo '   `',$x,'` ',$this->$x->get_db_type(),",n";
        }

        echo ");nn";
    }

    function make_form()
    {
        foreach ( get_class_vars($this->get_name()) as $x => $y)
        {
            echo $this->$x->label,': <',$this->$x->editor,' name="',$x,"\">n";
        }
    }

    function make_form_table()
    {
        echo "  <table class=\"mytable\">n";
        foreach ( get_class_vars($this->get_name()) as $x => $y)
        {
            echo '    <tr><th>',$this->$x->label,'</th><td><',
                $this->$x->editor,' name="',$x,'" value="'.$this->$x->value.
                "\"></td></tr>n";
        }
        echo "  </table>n";
    }
}

class Person extends Model
{
    var $name, $address, $phone;

    function __construct()
    {
        $this->name = new CharField(40, 'Name');
        $this->address = new CharField(40, 'Address');
        $this->phone = new CharField(15, 'Phone');
    }
}

$j = new Person();

$j->name->value = "Erkki Tapola";

$j->make_create_sql();

echo "<form action='.' method='POST'>n";
$j->make_form_table();
echo "</form>n";

?>

You can easily add more field types according to the example CharField. Other features also available in Django, but this example doesn’t (yet) implement:

• Query mechanisms to abstract SQL SELECT.
• Persistence; save mechanisms to abstract UPDATE and INSERT.
• Database table relation, fetch rows based on foreign keys and many-to-many relations

In addition, what I would like to see in Django:

• Methods to update the current database schema with the added and modified field information. (Note: Check out Django-evolution, which is doing exactly this, and it even maintains a history of modifications.

Such a functionality would be safe for added columns and even column truncation and removal, as long as you indicate that this is actually your intent.

This entry was posted on Friday, January 16th, 2009 at 19:17 and is filed under PHP, django, programming, tips, LinkedIn. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.