@classmethod
def from_sqla(cls, sqla_obj):
    """ Create a yalchemy ForeignKey from a sqlalchemy ForeignKeyConstraint

        Arguments:
            sqla_obj: The sqlalchemy ForeignKeyConstraint object.
        """
    assert len(sqla_obj.column_keys) == 1
    assert len(sqla_obj.elements) == 1
    target_table, target_col = sqla_obj.elements[0].target_fullname.rsplit('.',
        1)
    return cls(sqla_obj.column_keys[0], target_table, target_col)
