one2many field get row number - odoo-11

Question

I have a module contain one2many filed.
while I create data line in this o2m field, I'd like to append a row number to it.
I have try some method that I found in forum, like this link.
but since I have no function called _onchange_partner_id() , I don't know how to use it.
or this link .
but it seems like an old version method that I can't get well.
class YcWeight(models.Model):
_name = "yc.weight"
customer_detail_ids = fields.One2many("yc.weight.details", "name", "customer details")
class YcWeightDetails(models.Model):
_name = "yc.weight.details"
name = fields.Many2one("yc.weight", "weight detail list", ondelete="cascade")
no = fields.Integer("row number")
the "no" is a field that I want to show number of row count.
my problem is :
how can I get get the number of rows?
since onchage decorated function can't get data from db.

Answer 1

I find a solution by myself and it is simple:
use depends decorator.
class YcWeightDetails(models.Model):
_name = "yc.weight.details"
name = fields.Many2one("yc.weight", "weight detail list", ondelete="cascade")
no = fields.Integer("row number")
compuute_no = fields.Integer("invisible field", compute= "_get_row_no")
create a field "compuute_no" to compute.
#api.depends("compuute_no")
def _get_row_no(self):
if self.ids:
count =1
for rec in self:
weight_id = self.env['yc.weight.details'].search([('id','=', rec.id)])
weight_id.write({'no': count})
count+=1
or overwrite create method
#api.model
def create(self, vals):
main_key = self.env["yc.weight"].search([], order="id desc", limit=1).id
item_key = vals["name"]
if item_key and main_key == item_key:
number = len(self.env["yc.weight.details"].search([("name", "=", item_key)]))
vals.update({"no": number + 1})
return super(YcWeightDetails, self).create(vals)
hope it can help you.