Prestashop - calculated field in backoffice table form - module

Question

I would like to add a "virtual" field to a Prestashop 1.6 custom table in the back office. The field indice_calculo_pvp2 should not be saved into the database, as it is a calculated from the values of indice_calculo_pvp and precio_venta_recomendado. What would be the correct way to implement this?
My code is as follows :
public function renderList() {
$this->addRowAction('edit');
$this->addRowAction('delete');
$this->fields_list = array(
'id_product_price' => array(
'search' => false,
'title' => 'ID'
),
'precio_coste' => array(
'title' => 'Precio coste',
'search' => false,
'callback' => 'callback_format_price',
'suffix' => '€'
),
'indice_calculo_pvp' => array(
'title' => 'Indice de cálculo PVP',
'search' => false,
'callback' => 'callback_format_price',
'suffix' => '%'
),
'indice_calculo_pvp2' => array(
'title' => 'Indice de cálculo PVP2',
'search' => false,
'callback' => 'callback_calculate_pvp',
'suffix' => '%'
),
'precio_venta_recomendado' => array(
'title' => 'Precio de venta recomendado con IVA',
'search' => false,
'callback' => 'callback_format_price',
'suffix' => '€'
)
);
return parent::renderList();
}

Answer 1

Use calculation in your SQL SELECT query for the list. I don't know what your calculation formula and your SELECT query is but example of this:
$this->_select = 'a.indice_calculo_pvp / a.precio_venta_recomendado AS indice_calculo_pvp2';

Answer 2

You have 2 options:
You can use a callback function as in your code:
public function callback_calculate_pvp($id, $tr)
{
return $tr['indice_calculo_pvp'] * $tr['precio_venta_recomendado'];
}
You can use a virtual column in your field list indice_calculo_pvp2 and set the value in your SQL query or in getList override function (as ProductController do with price).
Good luck.