Hi,i have been put maximum effort on these i know these have been ask a lot and i have followed almost every post and i haven't achieve what i want

I have been trying to override _prepare_invoice function

so this is my sale.order.line (inherited) .py

class customSaleField(models.Model):
 _inherit = 'sale.order.line'
	
 TotalWeight = fields.Float(string='Total Weight',store=True)
 PricePerUnit = fields.Float(string='Price Per Unit',store=True)
 @api.onchange('product_uom_qty','product_id')
 def on_change_weight(self):
  if self.product_uom_qty:
   self.TotalWeight = self.product_uom_qty * self.product_id.weight
  
 @api.onchange('price_subtotal','TotalWeight','product_id','price_unit')
 def on_change_PricePerUnit(self):
  if self.price_subtotal:
   try:
    self.PricePerUnit = self.price_subtotal / self.TotalWeight
   except ZeroDivisionError:
    self.PricePerUnit = 0
 def _prepare_invoice(self):
  res = super(customSaleField,self)._prepare_invoice(self)
  if self.product_id:
   if self.TotalWeight:
    res['TotalWeight'] = self.TotalWeight
   if self.PricePerUnit
    res['PricePerUnit'] = self.PricePerUnit
  return res

I have followed this post and change the code structure to odoo10 it doesnt work 

it doesnt pass value up to account.invoice the value in the field are 0

https://www.odoo.com/zh_CN/forum/help-1/question/how-to-transfer-data-from-sale-order-to-invoice-when-clicking-on-create-invoice-85740

this is my account.invoice.line (inherited) .py

class customAccountField(models.Model):
 _inherit = 'account.invoice.line'
	
 TotalWeight = fields.Float(string='Total Weight',store=True)
 PricePerUnit = fields.Float(string='Price Per Unit',store=True)
 @api.onchange('quantity','product_id','invoice_line_ids')
 def on_change_weight(self):
  if self.quantity:
   self.TotalWeight = self.quantity * self.product_id.weight
 @api.onchange('price_subtotal','TotalWeight','product_id','price_unit','invoice_line_ids')
 def on_change_PricePerUnit(self):
  if self.price_subtotal:
   try:
    self.PricePerUnit = self.price_subtotal / self.TotalWeight
   except ZeroDivisionError:
    self.PricePerUnit = 0

in sale.order xml file

<odoo>
  <data>
<record model="ir.ui.view" id="sale_order_view_inherit"> 
    <field name="name">sale.order.view.inherit</field>
    <field name="model">sale.order</field>
    <field name="inherit_id" ref="sale.view_order_form"/>
    <field name="arch" type="xml"> 
        <xpath expr="/form/sheet/notebook/page/field[@name='order_line']/tree/field[@name='product_uom_qty']" position="after">
            <field name="TotalWeight"/>
   <field name="PricePerUnit"/>
        </xpath> 
    </field> 
 </record>
</data>
</odoo>

in account.invoice xml file

<odoo>
  <data>
<record model="ir.ui.view" id="account_view_inherit"> 
    <field name="name">account.view.inherit</field>
    <field name="model">account.invoice</field>
    <field name="inherit_id" ref="account.invoice_form"/>
    <field name="arch" type="xml"> 
        <xpath expr="/form/sheet/notebook/page/field[@name='invoice_line_ids']/tree/field[@name='quantity']" position="after">
            <field name="TotalWeight"/>
   <field name="PricePerUnit"/>
        </xpath> 
    </field> 
 </record>
</data>
</odoo>