I have some clothing items in different sizes such as small, medium or large. Now I want to manage each stock separately e.g. small 15, medium 25, large 30 without using configurable product option. Using this method I added quantity field in custom option and add quantity in database.  http://bhaskarchoubisa.blogspot.dk/2013/04/add-qty-box-in-custom-option-row-magento.html

Above link works perfect for me but the problem is arising on frontend, when we place an order of clothes in any size with any quantity, it will not decrease or update from our database. What should I do so that quantity can be decreased from our database?

I have some clothing items in different sizes such as small, medium or large. 

Now I want to manage each stock separately e.g. small 15, medium 25, large 30 without using configurable product option. Using this method I added quantity field in custom option and add quantity in database. 

Here is the link to add quantity in custom option in magento

Above link works perfect for me but the problem is arising on frontend, when we place an order of clothes in any size with any quantity, it will not decrease or update from our database.

What should I do so that quantity can be decreased from our database?

Any suggestions are very welcome! :)