The different "openerp model inheritance" mechanisms: what's the difference between them, and when should they be used ?

In OpenERP, there are 3 ways to inherit from an existing model:

  • _inherit = 'model' (without any _name)
  • _inherit = 'model' (with a specified _name)
  • _inherits = 'model'

What's the difference between them and, therefore, how to use them properly ?

Nicolas Bessi
Best Answer

This is a wide question:

In OpenERP we have many main type of inheritance:

Classical using Python inheritance.

It allows to add specific "generic" behavior to Model by inheriting classes that derive from orm.Model like geoModel that adds goegraphic support.

class Myclass(GeoModel, AUtilsClass):

Standard Using _inherit

The main objective is to add new behaviors/extend existing models. For example you want to add a new field to an invoice and add a new method: `

class AccountInvoice(orm.Model):
    _inherit = "account.invoice"
    _column = {'my_field': fields.char('My new field')}
    def a_new_func(self, cr, uid, ids, x, y, context=None):
        # my stuff
        return something


You can also override existing methods:`

def existing(self, cr, uid, ids, x, y, z, context=None):
    parent_res = super(AccountInvoice, self).existing(cr, uid, ids, x, y, z, context=context)
    # my stuff
    return parent_res_plus_my_stuff`

It is important to note that the order of the super call is defined by the inheritance graph of the addons (the depends key in

It is important to notice that _inherit can be a string or a list. You can do _inherit = ['model_1', 'model_2'].

List allows to create a class that concatenate multiple Model, TransientModel or better AbstractModel into a single new model.

So what about our '_name' property

  • If the _name as the same value as the inherited class it will do a basic inheritance.
  • If you forget to add the _inherit you will redefine the model
  • If your class _inherit one model and you set a _name different it will create a new model in a new database table.
  • If your class inherit many model you have to set _name if your override an existing model this way you may have some trouble, it should be avoided. It is better to use this to create new classes that inherit from abstract model.

Polymorphic data using _inherits

When using _inherits you will do a kind of polymorphic model in the database way.

For example product.product inherits product.template or res.users inherits res.partner. This mean we create a model that gets the know how of a Model but adds aditional data/columns in a new database table. So when you create a user, all partner data is stored in res_partner table (and a partner is created) and all user related info is stored in res_users table.

To do this we use a dict: _inherits = {'res.partner': 'partner_id'} The key corresponds to the base model and the value to the foreign key to the base model.

From here you can mix inheritance if you dare...

Hope it helps.

Vasiliy Birukov

What will happen when using _inherits we use the same _name?

Rick Leir

which is used mostly in OpenERP? which do you recommend?


Python default override class declaration, then how its works here ? Like product and stock module have class product declaration, where it do not overwrite previously declared class method and features ? How it keeps methods declared in other modules ?

Best Answer

This will help you to learn Different Types of Inheritance...