In this recipe, we will use the my_library add-on module from Chapter 4, Creating Odoo Add-On Modules.

Modify the library.book model, as shown in the following model definition:

class LibraryBook(models.Model):
    _name = 'library.book'

    name = fields.Char('Title', required=True)
    date_release = fields.Date('Release Date')
    pages = fields.Integer('Number of Pages')
    cost_price = fields.Float('Book Cost')
    category_id = fields.Many2one('library.book.category')
    author_ids = fields.Many2many('res.partner', string='Authors')

Add the library.book.category model. For simplicity, we will just add it to the same library_book.py file:

class BookCategory(models.Model):
    _name = 'library.book.category'

    name = fields.Char('Category')
    description = fields.Text('Description')

We will be using the library.book model and getting an average cost price per category.