问题
I have 3 models: Post, Comment, User
Post has many Comments
Comment belongs to User
User has field country_code
I want to get all post comments grouped by country code AND sorted by amount of comments per country.
This query:
post.comments.joins(:user).group("users.country_code").order('count_all desc').count
returns such kind of result:
{"DE"=>67,
"US"=>8,
"RS"=>8,
"IN"=>8,
"ES"=>7,
"BR"=>6,
...
"UA"=>0
}
What I need is a similar result where country codes are keys but values are arrays of comments. I don't know how to achieve this.
回答1:
You could use the group_by that comes with the Ruby enumeration module
post.comments.group_by{ |c| c.user.country_code }
If you also want it ordered by amount of comments in each group that's also possible:
post.comments.group_by{ |c| c.user.country_code }.sort_by{ |k, v| v.length }
I suppose to get the sorting in the opposite direction you could multiply the length by -1 in the sort block.
post.comments.group_by{ |c| c.user.country_code }.sort_by{ |k, v| v.length * -1 }
回答2:
Try something like this: (Un-tested):
post.comments.joins(:users).select("users.country_code, count(1) as count_all").group("users.country_code").order('count_all desc')
回答3:
I think if you use group by the grouping will occur in sql returning an aggregate result which won't have all of the comments. You should include user and then group in ruby. Something like this:
post.comments.includes(:users).inject({}){|r, x| r[x.user.country_code].nil? ? r[x.user.country_code] = [x] : r[x.user.country_code] << x;r}
来源：https://stackoverflow.com/questions/32254473/get-all-records-grouped-by-field-from-association-and-sorted-by-count-in-group