<h1>Onchange Method in Odoo</h1>

Onchange
The "onchange" mechanism provides a way for the client interface to update a form whenever the user has filled in a value in a field, without saving anything to the database.

For instance, suppose a model has three fields amount, unit_price and price, and you want to update the price on the form when any of the other fields is modified. To achieve this, define a method where self represents the record in the form view, and decorate it with onchange() to specify on which field it has to be triggered. Any change you make on self will be reflected on the form.

<!-- content of form view -->
<field name="amount"/>
<field name="unit_price"/>
<field name="price" readonly="1"/>

# onchange handler
@api.onchange('amount', 'unit_price')
def _onchange_price(self):
    # set auto-changing field
    self.price = self.amount * self.unit_price
    # Can optionally return a warning and domains
    return {
        'warning': {
            'title': "Something bad happened",
            'message': "It was very bad indeed",
        }
    }