In purchase order lines I want to have 2 fields either readonly or not depending on the product selected.

I understand how to determine which product is selected in the onchange function, but i don't know how to make those fields readonly.

I imagine it is something like:

res = {'value': {'price_unit': price_unit or 0.0, 'name': name or '', 'product_uom' : uom_id or False}, 'readonly': {'diameter': 1}

res = {'value': {'price_unit': price_unit or 0.0, 'name': name or '', 'product_uom' : uom_id or False}, 'attrs': {'diameter':[('readonly', True)],}}

But neither of these lines of code make the field diameter on the purchase order line read only.

What am I missing?