'Get the filter string value.
For \'server\' type filters this is saved in the session so that
it gets persisted across table loads.  For other filter types
this is obtained from the POST dict.'

def get_filter_string(self):

    filter_action = self._meta._filter_action
    param_name = filter_action.get_param_name()
    filter_string = ''
    if (filter_action.filter_type == 'server'):
        filter_string = self.request.session.get(param_name, '')
    else:
        filter_string = self.request.POST.get(param_name, '')
    return filter_string
