# -*- coding: utf-8 -*-
from odoo.exceptions import except_orm, Warning, RedirectWarning
from odoo import models, fields, api, _
from odoo.tools.translate import _
from odoo import SUPERUSER_ID, api
import odoo.addons.decimal_precision as dp
class sale_order_line(models.Model):    
    _inherit = 'sale.order.line'    
    qty_available = fields.Float(compute='product_qty_location_check', string='Quantity On Hand')    
    @api.multi    
    @api.depends('product_id', 'order_id.warehouse_id')    
    def product_qty_location_check(self):        
        for line in self:            
        qty = self.env['stock.quant'].search([('product_id', '=', line.product_id.id),('location_id', '=', line.order_id.warehouse_id.lot_stock_id.id)])            
        value = qty.quantity        
        self.qty_available = value


My form View.....

<?xml version="1.0" encoding="utf-8"?>
<odoo>   
    <data>      
        <record id="view_order_form" model="ir.ui.view">         
            <field name="name">Sale Order</field>         
            <field name="model">sale.order</field>         
            <field name="inherit_id" ref="sale.view_order_form" />         
            <field name="arch" type="xml">            
                <xpath expr="//tree/field[@name='price_unit']" position="before">               
                    <field name="qty_available"  groups="stock.group_stock_user"/>            
                </xpath>         
            </field>      
        </record>   
    </data>
</odoo>




Error while Installing/Updating Module

Traceback (most recent call last):
  File "/home/usman/odoo-dev/odoo/odoo/http.py", line 647, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/home/usman/odoo-dev/odoo/odoo/http.py", line 307, in _handle_exception
    raise pycompat.reraise(type(exception), exception, sys.exc_info()[2])
  File "/home/usman/odoo-dev/odoo/odoo/tools/pycompat.py", line 87, in reraise
    raise value
  File "/home/usman/odoo-dev/odoo/odoo/http.py", line 689, in dispatch
    result = self._call_function(**self.params)
  File "/home/usman/odoo-dev/odoo/odoo/http.py", line 339, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/home/usman/odoo-dev/odoo/odoo/service/model.py", line 97, in wrapper
    return f(dbname, *args, **kwargs)
  File "/home/usman/odoo-dev/odoo/odoo/http.py", line 332, in checked_call
    result = self.endpoint(*a, **kw)
  File "/home/usman/odoo-dev/odoo/odoo/http.py", line 933, in __call__
    return self.method(*args, **kw)
  File "/home/usman/odoo-dev/odoo/odoo/http.py", line 512, in response_wrap
    response = f(*args, **kw)
  File "/home/usman/odoo-dev/odoo/addons/web/controllers/main.py", line 934, in call_button
    action = self._call_kw(model, method, args, {})
  File "/home/usman/odoo-dev/odoo/addons/web/controllers/main.py", line 922, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/home/usman/odoo-dev/odoo/odoo/api.py", line 689, in call_kw
    return call_kw_multi(method, model, args, kwargs)
  File "/home/usman/odoo-dev/odoo/odoo/api.py", line 680, in call_kw_multi
    result = method(recs, *args, **kwargs)
  File "<decorator-gen-46>", line 2, in button_immediate_upgrade
  File "/home/usman/odoo-dev/odoo/odoo/addons/base/module/module.py", line 71, in check_and_log
    return method(self, *args, **kwargs)
  File "/home/usman/odoo-dev/odoo/odoo/addons/base/module/module.py", line 602, in button_immediate_upgrade
    return self._button_immediate_function(type(self).button_upgrade)
  File "/home/usman/odoo-dev/odoo/odoo/addons/base/module/module.py", line 541, in _button_immediate_function
    modules.registry.Registry.new(self._cr.dbname, update_module=True)
  File "/home/usman/odoo-dev/odoo/odoo/modules/registry.py", line 85, in new
    odoo.modules.load_modules(registry._db, force_demo, status, update_module)
  File "/home/usman/odoo-dev/odoo/odoo/modules/loading.py", line 339, in load_modules
    force, status, report, loaded_modules, update_module)
  File "/home/usman/odoo-dev/odoo/odoo/modules/loading.py", line 242, in load_marked_modules
    loaded, processed = load_module_graph(cr, graph, progressdict, report=report, skip_modules=loaded_modules, perform_checks=perform_checks)
  File "/home/usman/odoo-dev/odoo/odoo/modules/loading.py", line 134, in load_module_graph
    registry.setup_models(cr)
  File "/home/usman/odoo-dev/odoo/odoo/modules/registry.py", line 282, in setup_models
    model._setup_complete()
  File "/home/usman/odoo-dev/odoo/odoo/models.py", line 2397, in _setup_complete
    field.setup_triggers(self)
  File "/home/usman/odoo-dev/odoo/odoo/fields.py", line 685, in setup_triggers
    for model, field, path in self.resolve_deps(model):
  File "/home/usman/odoo-dev/odoo/odoo/fields.py", line 663, in resolve_deps
    field = model._fields[fname]
KeyError: 'warehouse_id'