'Return True if all columns in the given collection are
mapped by the tables referenced by this :class:`.Relationship`.'

def _columns_are_mapped(self, *cols):

    for c in cols:
        if ((self.secondary is not None) and self.secondary.c.contains_column(c)):
            continue
        if ((not self.parent.mapped_table.c.contains_column(c)) and (not self.target.c.contains_column(c))):
            return False
    return True
