Post.includes(:comments).order('timestamp DESC'.limit(5).to_a.size
返回 5 并生成以下 SQL 代码：
SELECT "posts".* FROM "posts" ORDER BY "posts"."timestamp" LIMIT 5
SELECT "comments".* FROM "comments" WHERE "comments"."commentable_type" = 'Post' AND "comments"."commentable_id" IN (517, 516, 515, 514, 513)
但是当我尝试添加评论排序时：
Post.includes(:comments).order('posts.timestamp DESC').order('comments.timestamp ASC').limit(5).to_a.size
它返回 1 并生成以下 SQL 代码：
SELECT DISTINCT "posts".id, posts.timestamp AS alias_0, comments.timestamp AS alias_1 FROM "posts" LEFT OUTER JOIN "comments" ON "comments"."commentable_id" = "posts"."id" AND "comments"."commentable_type" IN ('Post') ORDER BY posts.timestamp DESC, comments.timestamp ASC LIMIT 5
SELECT "posts"."id" AS t0_r0, "posts"."content" AS t0_r1, "posts"."timestamp" AS t0_r2, "comments"."id" AS t1_r0, "comments"."content" AS t1_r1, "comments"."timestamp" AS t1_r2, "comments"."commentable_id" AS t1_r3, "comments"."commentable_type" AS t1_r4 FROM "posts" LEFT OUTER JOIN "comments" ON "comments"."commentable_id" = "posts"."id" AND "comments"."commentable_type" IN ('Post') WHERE "posts"."id" IN (517, 517, 517, 517, 517) ORDER BY posts.timestamp DESC, comments.timestamp ASC
我认为第二种情况下的第一个查询应该看起来像第一种情况下的第一个查询。关于如何实施它的任何想法？