Reduce needless saves by avoiding setting _hasDataChanges flag

[colinmollenhour]

In some cases a setter is called just to store a reference to an object and not actually update the model data but it causes the model to be considered dirty thereby causing needles model saves. This tackles specific instances of this occurring but there is also a more holistic approach proposed in #1306.

This implements alternative changes proposed in #1306 (comment) and also an alternative solution to #1307

[woutersamaey]

Insta-like!

[fballiano]

since this is on v20 branch we should modify the README to add this PR to the "changes between v19 and v20" ;-)

[colinmollenhour]

I added a note to README so it dismissed approvals from @fballiano and @kiatng

[tmotyl]

why there is a double negation?

[fballiano]

it's a cast to boolean as far as I've read

[addison74]

I never used it but it is the equivalent (bool) $variables. Maybe the code with this variant !! should be modified to be more explicit for most and not to be able to search the Internet for the "double not" operator in PHP. A longer discussion exists here https://stackoverflow.com/questions/2127260/double-not-operator-in-php. Some people consider using it "fancy".

[colinmollenhour]

Sorry, this is a habit from writing C.. In PHP probably better to just use (bool) but they are functionally equivalent.

[github-actions]

Unit Test Results

1 files  ±0  1 suites  ±0   0s ⏱️ ±0s
0 tests ±0  0 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
7 runs  ±0  7 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit c450d45. ± Comparison against base commit f93c9e0.

[luigifab]

By adding:

public function setStockItem(Mage_CatalogInventory_Model_Stock_Item $stockItem)

Sorry, but there is:

magento-lts/app/code/core/Mage/CatalogInventory/Model/Stock/Status.php

Lines 494 to 498 in 90fb732

	/* back compatible stock item */
	foreach ($productCollection as $product) {
	$object = new Varien_Object(array('is_in_stock' => $product->getData('is_salable')));
	$product->setStockItem($object);
	}

And this produce:

Mage_Catalog_Model_Product::setStockItem(): Argument #1 ($stockItem) must be of type
Mage_CatalogInventory_Model_Stock_Item, Varien_Object given,
called in app/code/core/Mage/CatalogInventory/Model/Stock/Status.php on line 497

[fballiano]

I'll keep a tab with this PR open so that we don't forget about this problem...

[colinmollenhour]

@luigifab I just pushed a fix: #2208

[luigifab]

Another side effect, with Amasty_Promo_Model_Sales_Quote_Item, there is:
$stockItem = $this->_data['product']->_data['stock_item']->_data;

That produce: Undefined array key "stock_item"
Solution is to call directly getStockItem().

[addison74]

If we have a problem with this PR then it must be reported in Issues.

[luigifab]

No problem, but if another people encounter the same problem, I hope his preferred search engine will lead him here.