Is flat union chaining possible? Is it preferable to nested?

Question

Is flat union chaining possible? Is it preferable to nested?

bughit opened this issue 9 years ago · comments

[user_1.posts, user_2.posts, Post.published].inject(:union)

Nested

SELECT "posts".* FROM (
  SELECT "posts".* FROM (
    SELECT "posts".* FROM "posts"  WHERE "posts"."user_id" = 1
    UNION
    SELECT "posts".* FROM "posts"  WHERE "posts"."user_id" = 2
  ) posts
  UNION
  SELECT "posts".* FROM "posts"  WHERE (published_at < '2014-07-19 16:12:45.882648')
) posts

Flat

SELECT "posts".* FROM (
  SELECT "posts".* FROM "posts"  WHERE "posts"."user_id" = 1
  UNION
  SELECT "posts".* FROM "posts"  WHERE "posts"."user_id" = 2
  UNION
  SELECT "posts".* FROM "posts"  WHERE (published_at < '2014-07-19 16:12:45.882648')
) posts

Flat chaining strikes me as potentially less problematic at least for some engines than deep nesting. Is it possible to achieve that in the current version? Would it make sense to add this?

Something like: Relation.union(user_1.posts, user_2.posts, Post.published)

bughit · Answer 1 · Fri Sep 25 2015 02:01:02 GMT+0800 (China Standard Time)

looks like #4 enables this, do you plan on merging it?

bughit · Answer 2 · Tue Oct 06 2015 06:34:16 GMT+0800 (China Standard Time)

@brianhempel, what do you think of #4?

Brian Hempel · Answer 3 · Sun Mar 20 2016 10:58:29 GMT+0800 (China Standard Time)

Flatness would be great, but it's not easily supported by AREL right now so until that's improved it's going to be hacktastic to get it to work reliably in this gem.