Decrement value instead of setting it like `number = number - 1`. Is it possible in Magento?

Question

I need to decrement a value with an atomic database operation, is it possible using Magento models?

setNumber($number) works like number = $number, but I need it to be decremented in SQL query.

Is it possible in Magento or do I have to write the SQL query myself?

I'm voting to close this question as off-topic because it is about MYSQL — Sander Mangel, Feb 17 '15 at 13:55
@Sander-MageStackDay2015 It's not about MYSQL, I am asking if there is a Magento function that instead of setNumber(number) has something like decreaseBy(number) — tmm, Feb 17 '15 at 13:58

Fabian Schmengler · Accepted Answer · 2015-02-17T14:36:09.667

16

Yes, it's possible, using Zend_Db_Expr:

$object->setNumber(new Zend_Db_Expr('number-1'));

For reference:

The method Mage_Core_Model_Resource_Abstract::_prepareDataForSave() contains the following code:

if ($object->hasData($field)) {
    $fieldValue = $object->getData($field);
    if ($fieldValue instanceof Zend_Db_Expr) {
        $data[$field] = $fieldValue;
    } else {
        ... [normal value processing follows]

EAV Models:

Note that you only can reference the attribute by its name ("number" in the example) if it's a real column of the main table, not an EAV attribute.

Although the abovementioned method is only used by models with flat tables, Zend_Db_Expr can be used for EAV attributes as well, the method that handles it is Varien_Db_Adapter_Pdo_Mysql::prepareColumnValue().

BUT you always have use the column name "value":

$product->setNumber(new Zend_Db_Expr('value-1'));

You don't need to specify a table alias because during save each attribute gets processed with its own query, so "value" is not ambiguous.

edited Feb 17 '15 at 14:36

answered Feb 17 '15 at 14:19

Fabian Schmengler

65,791
25
187
421

/me sheds a tear... – benmarks Feb 17 '15 at 15:28
1

They are tears of joy. Great answer. – benmarks Feb 17 '15 at 15:56
And how does one do this with a collection? :) – philwinkle Feb 17 '15 at 20:24
There is no direct way to save attributes in a collection at once but you probably can do some clever stuff with $collection->getSelect() – Fabian Schmengler Feb 17 '15 at 20:45

Paras Sood · Answer 2 · 2015-02-17T14:07:21.100

0

try ->setNumber(getNumber() - $number)

Edit: This would be equivalent of Set number = number - X in mysql where X is $number.

If you want to do it in MySQL only then you just need to write a query.

edited Feb 17 '15 at 14:07

answered Feb 17 '15 at 14:00

Paras Sood

2,540
1
14
23

this will be number=some_number in sql query – tmm Feb 17 '15 at 14:01
write a sample query you want or an example...you aren't clear enough. – Paras Sood Feb 17 '15 at 14:03
UPDATE table SET number = number - 1 – tmm Feb 17 '15 at 14:06
See my updated answer..... – Paras Sood Feb 17 '15 at 14:07
your example would product UPDATE table SET number = 5 – tmm Feb 17 '15 at 14:10
I mean ->setNumber(getNumber() - $number) AND UPDATE table SET number = number - 1 would have the same result if $number value is 1. – Paras Sood Feb 17 '15 at 14:18
1

Technically, it's not because you can get race conditions. – Fabian Schmengler Feb 17 '15 at 14:41
The question is asking for an atomic database operation - which your solution is not. – Navarr Feb 17 '15 at 16:00
The question was edited to include atomic database operation after my answer :) – Paras Sood Feb 17 '15 at 20:40

Decrement value instead of setting it like `number = number - 1`. Is it possible in Magento?

2 Answers2

For reference:

EAV Models:

Linked

Related