Use of $installer v $this in install scripts

Question

Ok, using install scripts there seems to be a weird convention to use the following:

$installer = $this;

I really don't understand this as it is completely redundant.

Why not just use $this-> throughout the script?

Any ideas on why this convention exists?

Answer 1

The answer is much simpler. In 2007 (and I believe till 2009 when PhpStorm started rocking) no one IDE allowed to provide inline phpdoc for $this. But core developers wanted to have autocompletion in IDE. That's why they used these 2 lines:

$installer = $this;
/* @var $installer <appropriate class> */

Some modules have own setup class and it should have been used in inline phpdoc. But because setup/upgrade script were (and are) always created via "copy/paste some existing one and change" you can find maybe examples when module has own setup class (or uses eav setup model Mage_Eav_Model_Entity_Setup) but Mage_Catalog_Model_Resource_Setup is used in inline phpdoc in upgrade script.

Answer 2

The oldest version I have is 1.0. Even then $installer = $this; existed. Even in the files named upgrade-0.x.y-0.z.t this line exists.

In my opinion, when they started (I mean version 0.1 or something like that) they had something like $installer = new Something() and they decided to change the logic.
I assume this because of the <class> tag in the config.xml of some modules (Mage_Catalog for example). Versions before 1.6:

<setup>
    <module>Mage_Catalog</module>
    <class>Mage_Catalog_Model_Resource_Eav_Mysql4_Setup</class>
</setup> 

Or in versions 1.6+ :

<setup>
    <module>Mage_Catalog</module>
    <class>Mage_Catalog_Model_Resource_Setup</class>
</setup>

I usually use $this instead of $installer and I didn't have any issue (if that maters in any way).

Answer 3

This is a convention of unknown and possibly dubious logic present since the earliest public beta from 2007 (Preview B1 0.6.12383; login required).

It is used as a convention to ensure that the class which is executing setup code is consistently aliased in setup scripts. For example, while both the Enterprise_GiftWrapping and Enterprise_Rma modules have their own setup classes, they each alias $installer to an instance of Mage_Catalog_Model_Resource_Setup when adding attributes to the product entity, e.g.:

app/code/core/Enterprise/GiftWrapping/sql/enterprise_giftwrapping_setup/install-1.11.0.0.php

<?php

$installer = $this;
/* @var $installer Enterprise_GiftWrapping_Model_Resource_Setup */
//... miscellaneous Enterprise_GiftWrapping setup logic

$installer = Mage::getResourceModel('catalog/setup', 'catalog_setup');
//... miscellaneous product entity attribute manipulation

Answer 4

One thing I like about using $installer that I really want to add is that it makes it easy to replace it with something else or to run it outside of the class scope.

1. Replacing it:

$installer = $this;
/* @var $installer Mage_Core_Model_Resource_Setup */
// Do basic stuff

$installer = Mage::getSingleton('eav/entity_setup', 'eav_setup');
/* @var $installer Mage_Eav_Model_Entity_Setup */
/// Do stuff with attributes

2. Outside scope:

$ php -a
php > require_once 'app/Mage.php';
php > Mage::init();
php > require 'app/code/local/Vendor/Module/data/vendormodule_setup/data-upgrade-0.1.1-0.1.2.php';
Upgrade worked!
Debug data dump: array(4) {
  'id' =>
  int(123)
  'foo' =>
  string(3) "bar"
}

Of course with data-upgrade-0.1.1-0.1.2.php having:

//$installer = $this;
$installer = Mage::getResourceSingleton('core/setup', 'vendormodule_setup');
/* @var $installer Mage_Core_Model_Resource_Setup */

// Do lots of stuff ...

echo "Upgrade worked!\n";
echo "Debug data dump: ";
var_dump($debug);

So this prevents Fatal error: Using $this when not in object context

Answer 5

I would guess it is from earlier days (<v.1.1). But to be honest, I have no idea. I think it is a bit better readable...

We have always done it like this

You know ;-)