How to do it...

We will edit the LibraryBook class in the models/library_book_categ.py Python file:

1. To create the database constraint, add a model attribute:

class LibraryBook(models.Model): 
    # ... 
    _sql_constraints = [ 
        ('name_uniq', 
         'UNIQUE (name)', 
         'Book title must be unique.') 
        ] 

2. To create the Python code constraint, add a model method:

from odoo import api 
class LibraryBook(models.Model): 
    # ... 
    @api.constrains('date_release') 
    def _check_release_date(self):
    for record in self:
        if (record.date_release and
                record.date_release > fields.Date.today()):
            raise models.ValidationError(
                'Release date must be in the past')                                  

After these changes are made to the code file, an addon module upgrade and server restart are needed.