Sorry , but what I am looking for is how to make relation in the same model.

I have a model called Person inheriting from res.partner like that. I know that the relation ono2one is not available anymore.

So i choose to make a many2one field.And i want when i change the married_with field for the person x, , it will change for person y

class Person(models.Model):
    _name = 'res.partner'
    _inherit = 'res.partner'
    married_with = fields.Many2one('res.partner', ondelete='set null', string='Conjoint', index=True)

You

When you change for example   the client, you want to change it with another field

1- You can link it to Related

for example 

    partner_id = fields.Many2one('res.parner', string="Partner")
    phone = fields.Char( string="Identification", related='partner_id .phone')

  phone This field is present in the model 'res.parner' 

2- the other solution by fuction On_change 

@api.onchange('partner_id')
def on_change_field(self):
    self.phone = self.partner_id.phone

This should give you a clue:

field_of_other_obj = fields.Many2one('referencing.object')

@api.onchange('field_of_object')
def get_changes(self):
    if self.field_of_object:
        self.field_of_other_obj = self.field_of_object.pointed_field_obj

Make sure the "field_of_other_obj" model is the same with the pointed_field_obj.

If you need more clarity, feel free to ask with what you have done (code).