When writing Odoo models, it is often the case that some fields are interrelated. We looked at how to specify constraints between fields in the Adding constraint validations to a model recipe in Chapter 5, Application Models. This recipe illustrates a slightly different concept. Here, onchange methods are called when a field is modified in the user interface to update the values of other fields of the record in the web client, usually in a form view.

We will illustrate this by providing a wizard similar to the one defined in the Writing a wizard to guide the user recipe, but that can be used to record book returns. When a member is set in the wizard, the list of books is updated to the books that are currently borrowed by the member. While we are demonstrating onchange methods on a TransientModel, these features are also available on normal Models.