'Implicit join (Query) for this field, for backwards-compatibility'

@property
def join(self):

    if (self._join is not None):
        return self._join
    join = self._join = {}
    for (tablename, joins) in self._joins.items():
        query = None
        for expression in joins:
            if (query is None):
                query = expression.second
            else:
                query &= expression.second
        if query:
            join[tablename] = query
    return join
