Development Book V18: Inheritance

Inheritance is a key mechanism in modular development that enables customization and extension of existing components without altering the original source code. It allows developers to build on top of standard functionality, whether in models, views, or other elements, ensuring clean, maintainable, and upgrade-safe customizations.

There are mainly two types of inheritance used in Odoo:

• Model Inheritance (including Classical, Prototype, and Delegation)
• View Inheritance

Classical Inheritance

Classical inheritance is used to create a new model that inherits all fields and behavior from a base model, while also allowing additional fields or method overrides.

from odoo import models, fields

class ParentModel(models.Model):
    _name = 'parent.model'

    name = fields.Char(string="Name")


class ChildModel(models.Model):
    _name = 'child.model'
    _inherit = 'parent.model'

    date = fields.Date(string="Date")

• ChildModel now includes both the name and date fields.
• You can override or extend existing methods from the parent model.
• This creates a new database table for child.model.

Prototype Inheritance

Prototype inheritance is a technique that allows developers to enhance an existing model by adding new fields or methods to it—without creating a new model or database table. This approach essentially reuses and extends an existing model’s structure, a process commonly referred to as prototyping.

In this type of inheritance, only the _inherit attribute is required. By omitting the _name attribute, you directly modify the original model. The system treats the extended version as the most recent definition of the model, incorporating both its original and new features.

from odoo import models, fields

# Parent Model
class ParentModel(models.Model):
    _name = 'parent.model'

    name = fields.Char(string="Name")


# Prototype Inheritance - Modifying the Parent Model
class InheritParentModel(models.Model):
    _inherit = 'parent.model'

    date = fields.Date(string="Date")

• The ParentModel defines the base structure with a name field.
• The InheritParentModel adds a new field date to the existing parent.model.
• Since no _name is defined in the second class, it doesn’t create a new model or table.
• The parent.model now includes both name and date fields, as if they were part of the same original definition.
• You can also override or extend methods using this approach.

Delegation Inheritance

Delegation inheritance allows you to reuse the fields and behavior of an existing model without subclassing. It creates a one-to-one relation via _inherits.

from odoo import models, fields

# Parent Model
class ProductTemplate(models.Model):
    _name = "product.template"

    name = fields.Char(string="Name")


# Child Model with delegation inheritance
class ProductProduct(models.Model):
    _name = "product.product"
    _inherits = {'product.template': 'product_tmpl_id'}

    product_tmpl_id = fields.Many2one(
        'product.template', 
        string='Product Template', 
        required=True, 
        ondelete="cascade", 
        auto_join=True,
        index=True
    )

• The product.product model delegates access to all fields from product.template via product_tmpl_id.
• Used when two models are tightly related but still separate.
• Affects the behavior and schema differently from _inherit.

View Inheritance

View inheritance is used to extend, modify, or reorganize existing views like forms, kanban, tree, etc. It relies on the inherit_id field in XML and uses XPath expressions.

    product.view.form.inherit.custom.module
    product.template
    
    
        
            
        
    

• inherit_id links this view to the original one.
• XPath selects elements in the base view using expr, then you can insert or modify elements:
• position="before": insert before the node.
• position="after": insert after the node.
• position="inside": insert as a child.
• position="replace": replace the node.