I have two model and code is given below 

class SellProduct (models.Model): 
    _name = 'sell.product'
     _rec_name = 'product_seq' 
# def product (self):     # name = self.env ['product.create']. search ([])     # print (name ) product_seq = fields.Many2one ( comodel_name = "product.create" , string = "Product ID" , required = False ,)     product_name = fields.Char ( related = 'product_seq.product_name' , string = "Product Name" ,required = False ,)
    



    

    sell_product_quantity = fields.Integer ( string = "Product Quantity" , required = True ,) 
    gold_price_new = fields.Integer ( string = "Total Price" , compute = 'compute_price' , store = True ,) 

    payment = fields.Integer ( string = "Payment" ) 
    due_amount = fields.Integer (string = "Due" , compute = 'due_compute' , store = True ) 
    company_id = fields.Many2one ( 'res.company' , 'Company' , required = True , index = True , 
                                 default = lambda self: self.env.company .id) 
    currency_id = fields.Many2one ( "res.currency" , string = "Currency" , readonly = True , 
                                  default = lambdaself: self.env.company.currency_id.id, required = True ) 

    sell_line = fields.Many2one ( comodel_name = "product.create" , string = "Sell Line" , required = False ,)

class ProductCreate (models.Model): 
    _name = 'product.create'
     _inherit = [ 'mail.thread' , 'mail.activity.mixin' ,] 
    _rec_name = 'product_seq' 
@ api.depends ( 'create_sell_line' , 'create_sell_line. sell_product_quantity ' ) def update_value ( self ): for rec in self :             rec.product_quantity_new = rec.create_sell_line.sell_product_quantity     product_seq = fields.Char ( string = ' PID ' ,required =
    
    
        


True , copy = False , 
                              randomly = True , index = True , 
                              default = lambda self: _ ( 'New' )) 
    product_name = fields.Char ( string = "Product Name" ) 
    product_image = fields.Binary ( string = "Product Image " ) 
    product_quantity_new = fields.Integer ( compute = 'update_value' ) 
    product_quantity = fields.Integer ( string = "Product Quantity" ,) 
    gold_quality = fields.Selection ( string = "Gold Quality" , selection = [( '18k' , '18K' ), ( '21k' , '21K' ), ( '22k' , '22K' )], 
                                    required = True ,) 
    gold_rate = fields.Integer ( string = "Gold Rate" ) 
    gold_weight = fields.Float ( string = "Weight / Gram" , required = True )
    making_cost = fields.Integer ( string = " Making Cost") 
    gold_price = fields.Integer ( string = "Sub-total Price" , compute = 'compute_sub_total_price' , store = True ) 
    tax = fields.Integer ( string = "Tax" , ) 
    tax_cal = fields.Integer ( string = "tax Calculation" , compute = 'compute_tax' , store = True ) 
    total_cost = fields.Integer ( string= "Total Price" , compute = 'compute_total_price' , store = True ) 

    create_sell_line = fields.One2many ( comodel_name = "sell.product" , inverse_name = "sell_line" , string = "create sell line" , 
                                       required = False ,)

Fom  sell.product model, sell_product_quantity field's value will be store product.create model's prouct_quantity_new field
How to solve this problem?