Magento set the new attribute value - php

Question

I have created a new IMEI attribute of type textarea for all products, see from the image. Can anyone point out a function to update the its value. I have the code like the following.
$this belogns to Mage_Sales_Model_Order.
foreach ($this->getAllItems() as $item) {
$item->setImei('123');
$item->save();
echo $item->getImei();
}
I am getting 123 from the last statement but when I am viewing from admin. Its not changing there. Also in which table the attribute and value will be stored, So I can debug from there.

Answer 1

What class is $this->getAllItems() is it Mage_Catalog_Model_Product?
If it not Mage_Catalog_Model_Product then load the product by id and save the product
foreach ($this->getAllItems() as $item) {
$product = Mage::getModel('catalog/product')->load($item->getId() or $item->getProductId())
$product->setImei($product->getImei() . '123');
$product->save();
}

Answer 2

The values of catalog product attributes of type text are stored in the table catalog_product_entity_text. An SQL would be
select * from catalog_product_entity_text where attribute_id = {insert your attribute id} and entity_id = {insert your product id}
The query will return results for every store view in the system.
The reason why you do not see a change to the attribute in the backend is probably because the new value is set for a different website/store than the one loaded in the backend.
You are already using a correct way to set the attribute value assuming $item is of type Mage_Catalog_Model_Product:
$item->setImei('123');
$item->save();

Answer 3

heres how you do it differently: (color = attribute name, red = attribute value id)
starts assuming you already have $product available.
$attr = $product->getResource()->getAttribute('color');
if ($attr->usesSource()) {
$avid = $attr->getSource()->getOptionId('red');
$product->setData('color', $avid);
$product->save();
}