Hi friends, This code worked for me.Make use of it

def _get_expense_id(self, cr, uid, context=None):

     result = []

     if context is None:

         context = {}

     name = ["Selling Expenses","Grading Expenses","Stock Maintenance Expenses", "Fumigation Charges"]

     expense_obj = self.pool.get('expense.deduct')

     res = expense_obj.search(cr, uid, [('name', '=', name )])

     for eachid in res:

        result.append(eachid)

     return result or result[0] or False

     _defaults = { 'expense_deduct_id': _get_expense_id, }

it does not work when you set the default value for that field in the related model?