1. Add a One2many field in the sale.order model to store the temporary sale order lines.

2. Modify the onchange method to add the temporary sale order lines to the One2many field.

3. When converting the quotation to a sales order, copy the temporary sale order lines from the One2many field to the actual sale order lines.

Here's the updated code:

1. Add a One2many field in the sale.order model:

class SaleOrder(models.Model):

_inherit = 'sale.order'

temp_order_lines = fields.One2many('sale.order.line', 'order_id_temp', string='Temporary Order Lines')

Modify the onchange method to add the temporary sale order lines to the temp_order_lines field:

@api.onchange('default_product_line')

def add_temp_order_lines(self):

temp_lines = []

for line in self.default_product_line:

temp_lines.append((0, 0, {

'name': line.name,

'product_uom_qty': line.qty,

'price_unit': line.price_unit,

'product_id': line.product_id.id

}))

self.temp_order_lines = temp_lines

When converting the quotation to a sales order, copy the temporary sale order lines to the actual sale order lines:

def convert_to_sales_order(self):

# Create the sales order

sale_order_vals = {

# Add other required fields for the sales order

}

sale_order = self.env['sale.order'].create(sale_order_vals)

# Copy temporary sale order lines to actual sale order lines

for temp_line in self.temp_order_lines:

sale_order_line_vals = {

'order_id': sale_order.id,

'name': temp_line.name,

'product_uom_qty': temp_line.product_uom_qty,

'price_unit': temp_line.price_unit,

'product_id': temp_line.product_id.id,

# Add other required fields for the sales order line

}

self.env['sale.order.line'].create(sale_order_line_vals)

# Optionally, you can remove the temporary sale order lines from the quotation

self.temp_order_lines = [(5, 0, 0)]

return sale_order

Here is how you could do it

      self.write({'order_line': [(0,0, {

            'name': line.name,

            'product_uom_qty': line.qty,

            'price_unit': line.price_unit,

            'product_id': line.product_id.id

      })]})

The idea it's that you don't need to create anything in the database, since it's an onchange you need to return the change of the data. In this case you are adding a new line to the sale order that will be showing in the browser and saved into the database once you save the sale order form