Bulk Update One2Many odoo Just Change 1 data From API response

i create API with Odoo for consume in web apps, my problem it's when i bulk update from web apps which has form like this

and From clint side i got response JSON like this

[{"product_char": "A", "quantity": "1", "price_unit": "100"},
{"product_char": "M", "quantity": "1", "price_unit": "100"}]

and in the odoo controller this is my function :

@http.route([
    '/api/update/petty_cash/<int:id>'
], type='http', auth="none", methods=['POST'], csrf=False)
@check_valid_token
def update_petty_cash(self, id, **rec):
    # import pdb;pdb.set_trace()
    user_id = request.uid
    petty_cash = request.env['petty.cash.app'].\
        search([('create_uid', '=', user_id),
                ('id', '=', id)
                ])

    image_file = rec.get("image", False)
    replace = image_file.replace(" ", "+")
    user_id = request.uid
    petty_cash.write({
        'reference': rec['reference'],
        'partner_id': rec['partner_id'],
        'state': petty_cash.state,
        'request_by': user_id,
        'date_requested': fields.Date.today(),
        'image': replace,

    })

    petty_cash_line = request.env['petty.cash.line'].sudo().search([('pety_cash_id', '=', petty_cash.id)])
    for product in eval(rec['products']):
        petty_cash_line.update({
            'pety_cash_id': petty_cash.id,
            'product_char': product['product_char'],
            'quantity': product['quantity'],
            'price_unit': product['price_unit'],
        })

    return valid_response(
        200, {
            "msg" : "Data Updated",
            # "data": petty_cash,
        }
    )

i have been looping in section bulk update data like this :

petty_cash_line = request.env['petty.cash.line'].sudo().search([('pety_cash_id', '=', petty_cash.id)])
    for product in eval(rec['products']):
        petty_cash_line.update({
            'pety_cash_id': petty_cash.id,
            'product_char': product['product_char'],
            'quantity': product['quantity'],
            'price_unit': product['price_unit'],
        })

    return valid_response(
        200, {
            "msg" : "Data Updated",
            # "data": petty_cash,
        }
    )

but data product_char in database just write 1 data, just value M changed data, whereas i get 2 value product_char from client side A and M,

this is result when i print eval(rec['products'])

i just want update data in 'petty.cash.line' model , data needs to update is :
1. product_char
2. quantity
3. price_unit

relation one2Many 'petty.cash.app' with 'petty.cash.line' is field:

 pety_cash_line_ids = fields.One2many('petty.cash.line', 'pety_cash_id', string='Pety Cash Lines', copy=True)

relation many2one 'petty.cash.line' with 'petty.cash.app' is field:

 pety_cash_id = fields.Many2one('petty.cash.app', string="Pety cash")

i have been change update method, to write method in odoo, but result is same, just write 1 data, whats wrong from my code ? please help

Thanks

Change this code

petty_cash_line = request.env['petty.cash.line'].sudo().search([('pety_cash_id', '=', petty_cash.id)])
    for product in eval(rec['products']):
        petty_cash_line.update({
            'pety_cash_id': petty_cash.id,
            'product_char': product['product_char'],
            'quantity': product['quantity'],
            'price_unit': product['price_unit'],
        })

to

petty_cash_line = request.env['petty.cash.line'].sudo().search([('pety_cash_id', '=', petty_cash.id)])
products = eval(rec['products'])
for index, line in enumerate(petty_cash_line):
  line.update({
    'product_char': products[index]['product_char'],
    'quantity': products[index]['quantity'],
    'price_unit': products[index]['price_unit'],
})

That should get it to work because we loop update each line with its corresponding product from client.