base.py 文件源码

def _get_nonansi_join_whereclause(self, froms):
        clauses = []

        def visit_join(join):
            if join.isouter:
                def visit_binary(binary):
                    if binary.operator == sql_operators.eq:
                        if join.right.is_derived_from(binary.left.table):
                            binary.left = _OuterJoinColumn(binary.left)
                        elif join.right.is_derived_from(binary.right.table):
                            binary.right = _OuterJoinColumn(binary.right)
                clauses.append(visitors.cloned_traverse(
                    join.onclause, {}, {'binary': visit_binary}))
            else:
                clauses.append(join.onclause)

            for j in join.left, join.right:
                if isinstance(j, expression.Join):
                    visit_join(j)
                elif isinstance(j, expression.FromGrouping):
                    visit_join(j.element)

        for f in froms:
            if isinstance(f, expression.Join):
                visit_join(f)

        if not clauses:
            return None
        else:
            return sql.and_(*clauses)