Odoo Development: Prevent deletion with custom constraint

By default Odoo asks for confirmation if a record is being deleted. Making validations before deletion is up to the developer. I will show how you can add a custom constraint that prevents a record being deleted.

The examples are based on the Odoo App Certificate Planner.

In our scenario a record from model post_certification_item can only be deleted if the field change_id is not set.

Extend the default unlink (aka delete) method.

models/post_certification_item.py

from odoo import models, fields
from odoo.exceptions import UserError

class PostCertificationItem(models.Model):
    ...
	
    def unlink(self):
        if self.change_id:
            raise UserError(_('You cannot delete a Post Certification Item that links to a Change.'))
        return super(PostCertificationItem, self).unlink()

If you try to delete a record that links to a change and confirm the prompt, this message will pop up: