Hi, there,

Target:

Process:

1. XML(this editor is hard to use)

    res.partner
    
    
        
            
            
            
        
    

2.py

@api.onchange('state_id')
def _onchange_state_id(self):
    self.city_id = None
    self.district_id = None
    if self.state_id:
        return {'domain': {'city_id': [('state_id', '=', self.state_id.id)]}}
    else:
        return {'domain': {'city_id': []}}

from odoo import fields, models

class District(models.Model):
    _name = 'res.country.district'
    _description = 'District'
    _order = 'name'

    name = fields.Char("Name", required = True)
    city_id = fields.Many2one(
        'res.country.city', 'City'
    )

class City(models.Model):   
    _name = 'res.country.city'
    _description = 'City'
    _order = 'name'

    name = fields.Char("Name", required=True, translate=True)
    zipcode = fields.Char("Zip")
    state_id = fields.Many2one(
        'res.country.state', 'State')