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

[bughit]

[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]

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

[bughit]

@brianhempel, what do you think of #4?

[brianhempel]

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.

See also discussion on #4 .