Adding computed fields to a model

Sometimes, we need to have a field that has a value calculated or derived from other fields in the same record or in related records. A typical example is the total amount, which is calculated by multiplying a unit price by a quantity. In Odoo models, this can be achieved using computed fields.

To show you how computed fields work, we will add one to the Library Books model to calculate the days since the book's release date.

It is also possible to make computed fields editable and searchable. We will implement this to our example as well.

Getting ready

We will continue using the my_library add-on module from the previous recipe.

How to do it...

We will edit the models/library_book.py code file to add a new field and the methods supporting its logic:

1. Start by adding the new field to the Library Books model:

   class LibraryBook(models.Model): 
       # ... 
       age_days = fields.Float...