i have two class x and y

class x_obj(osv.osv):

   _columns ={

        fields ..........

      x_id:fields.many2one('y.obj')

                 }

x_obj() 

class y_obj(osv.osv):

_columns ={

fields ..........

y_id:fields.one2many('x.obj', 'x_id', 'x_child'),

}

y_obj()

I have form view that retrieves all records in x_obj table based on certain condition 

but what i am facing is i don't want a new record to be created in x_table except y_obj's reference only to be updated in existing x_object table records when i save the record in y_obj, and how can really retrieve child x_obj's id through  y_id field i can access all fields but i couldn't get x_obj's id through one2many field reference