<notebook>                        <page string="Order Lines">                            <field name="order_line" widget="one2many_list" context="{'default_order_id': active_id}">                                <tree editable="bottom">                                    <field name="product_id"/>                                    <field name="product_uom_qty"/>                                    <field name="price_unit" attrs="{'readonly': [('product_id', '!=', False)]}" />                                    <field name="price_subtotal" readonly="1"/>                                    <field name="company_id" invisible="1"/>                                </tree>                            </field>                        </page>                    </notebook>





I want to make the price_unit field not change its contents even though the quantity and subtotal contents change, if I enter a different number in the quantity then the price_unit changes to 0. How do I do this so that after entering an item, the price_unit always shows the price of the item without changing?