'Add a filter condition to a query based on the inputs.
Args:
identifier: name of the property (or self.__ANCESTOR for ancestors)
condition: test condition
value: test value passed from the caller
query: query to add the filter to'

def __AddFilterToQuery(self, identifier, condition, value, query):

    if (identifier != self.__ANCESTOR):
        filter_condition = ('%s    %s' % (identifier, condition))
        logging.log(LOG_LEVEL, 'Setting    filter    on    "%s"    with    value    "%s"', filter_condition, value.__class__)
        datastore._AddOrAppend(query, filter_condition, value)
    else:
        logging.log(LOG_LEVEL, 'Setting    ancestor    query    for    ancestor    %s', value)
        query.Ancestor(value)
