Hi all,

i'm reading about "delegation inheritance" in "Odoo 10 Developments essentials" book.

In the example there is:

```

from odoo import Model, fields

class User(models.Model):

    _name="res.users"

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

    partner_id = fields.Many2one("res.partner")

```

in this example I don't know why there is M20 in "partner_id" field.

I agree that to a user corresponds only one "res_partner" but I don't understand why to a "partner" can correponds many users.

Anyone can help me to understand?