Hi, This is follow-up work to patch [1], which fixed a bug when altering a CHECK constraint's enforceability. The fix was not very elegant. It had to use upward recursion to traverse all ancestors when deciding a child table's enforceability. This was because the existing function find_all_inheritors() returns a list of descendants without ensuring that parents precede their children.
This patch introduces a new function, find_all_inheritors_ordered(), which
guarantees that every ancestor in the returned list appears before its
descendants. With this new function, the original fix in commit 0cd17fdd3c0 is
significantly simplified. The function could also potentially benefit other
features that need to traverse inheritance trees in parent-before-child order.
This patch also strengthens an existing test by adding another level of
inheritance. My first version of the implementation failed with the following
case:
```
Root ———————————————> child
\ /
\ ——————> a —————> b /
```
(The diagram might not display well. Basically, “child" has parents “b" and
“root", “b" has parent “a”, “a” has parent “root")
The current version uses Kahn's topological sorting algorithm, which handles
this case correctly. Please see the attached patch for details.
[1] https://postgr.es/m/[email protected]
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
v1-0001-Add-find_all_inheritors_ordered.patch
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