Understanding OnDelete Policies in Odoo 18

Odoo 18 introduces powerful tools for database management, and one of the essential features for developers to understand is the ondelete policy. This mechanism plays a critical role in managing how related records are handled when a parent record is deleted. Whether you’re managing simple models or complex relationships, grasping the concept of ondelete policies ensures data consistency and prevents unexpected issues in your Odoo applications.

What is ondelete in Odoo?

The ondelete parameter is used in relational fields such as Many2one, One2many, and Many2many to define the behavior of child records when a parent record is deleted. It helps maintain referential integrity in the database by specifying what action should be taken on the related records.

For example, consider a Many2one relationship between an Order model and a Customer model:

class Order(models.Model):
    _name = 'my_module.order'

    name = fields.Char(string="Order Reference")
    customer_id = fields.Many2one(
        'my_module.customer', string="Customer", ondelete='cascade'
    )

In this case, the ondelete policy dictates what happens to orders when a customer is deleted

Available ondelete Policies

Here are the most common ondelete policies you can use in Odoo:

1. cascade

• Deletes the child records when the parent record is deleted.
• Use case: You want to ensure no orphaned records remain.
• Example:

customer_id = fields.Many2one('res.partner', ondelete='cascade')

2. set null

• Sets the value of the relational field to NULL in the child records when the parent record is deleted.
• Use case: You want the child records to remain but without a link to the deleted parent.
• Example:

customer_id = fields.Many2one('res.partner', ondelete='set null')

3. restrict

• Prevents the deletion of the parent record if there are related child records.
• Use case: You want to enforce a strict dependency between parent and child records
• Example:

customer_id = fields.Many2one('res.partner', ondelete='restrict')

4. set default

• Sets the relational field to a default value when the parent record is deleted.
• Use case: You want to replace the deleted parent with a default value in child records.
• Example:

customer_id = fields.Many2one('res.partner', ondelete='set default')

5. no action

• Does nothing to the child records when the parent record is deleted. This is the default behavior if no ondelete is specified.
• Use case: You want complete control over the behavior through custom logic.
• Example:

customer_id = fields.Many2one('res.partner', ondelete='no action')

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Practical Scenarios:

1. Managing Orders and Customers: If a customer is deleted, their orders should also be removed to avoid orphaned records:

customer_id = fields.Many2one('res.partner', ondelete='cascade') 

• Employee and Manager Relationship: If a manager is deleted, employees should remain but without a link to the manager:

manager_id = fields.Many2one('hr.employee', ondelete='set null')

• Prevent Deletion of Records with Dependencies: To prevent deleting a product category if products are assigned to it:

category_id = fields.Many2one('product.category', ondelete='restrict')