Difference Between _inherit  vs _inherits in Odoo


✅ What Are They?

Both _inherits and _inherit are used to extend existing models in Odoo, but they work differently:


Feature

_inherit

_inherits

Inheritance

Classical Odoo inheritance

Delegation inheritance

DB Structure

Works on same table (shared)

Works on multiple tables (linked)

Use Case

Extend behavior or add fields

Compose new models using others

Field Access

Direct

Delegated via foreign key



1. _inherit: Classic Inheritance

📌 Use Case:

Used when you want to add fields or override logic in an existing model like res.partner, sale.order, etc.


🔧 Example:


class InheritPartner(models.Model):

    _inherit = 'res.partner'

​

    loyalty_points = fields.Integer(string="Loyalty Points")

​

    def custom_method(self):

        # extending existing method

        pass


✅ This will add a new field directly to the res.partner table.


2. _inherits: Delegated Inheritance

📌 Use Case:

Used when you want to reuse another model's fields and data but store your own fields in a separate table.


🔧 Example:


class StudentRecord(models.Model):

    _name = 'student.record'

    _inherits = {'res.partner': 'partner_id'}


    partner_id = fields.Many2one('res.partner', required=True, ondelete='cascade')

    student_code = fields.Char(string='Student Code')


✅ This allows you to:

  • Store student-specific data in student.record
  • Reuse all res.partner fields as if they belong to student.record

So:

student = self.env['student.record'].browse(1)

print(student.name)  # from res.partner

print(student.student_code)  # from student.record


⚠️ The record will be stored in two tables, linked by the partner_id.



🎯 When to Use What?


Use Case

Use _inherit

Use _inherits

Extend existing model’s features

✅ Yes

🚫 No

Combine models like composition

🚫 No

✅ Yes

Need separate table and identity

🚫 No

✅ Yes

Add or override methods

✅ Yes

🚫 Limited



⚙️ Internal Difference


Feature

_inherit

_inherits

Field resolution

From current model/table

Redirected to foreign model via M2O

Record identity

Same record ID and table

Separate IDs (joined by foreign key)

DB schema

Fields added directly to base model

Separate table with relationship



✅ Summary Table


Attribute

Purpose

Storage

Real Use Case

_inherit

Extend existing model (fields/methods)

Shared table

Add extra fields to res.partner

_inherits

Reuse another model with linkage

Separate table

Create student.record from partner



🧠 Developer Tips

  • Use _inherit for 90% of extension work.
  • Use _inherits only when modeling something structurally distinct but sharing core data.
  • Avoid mixing both in the same model unless explicitly required.
  • Be careful with record deletion in _inherits – always set ondelete='cascade' for clean joins.