Filter by count of children using Rails 3

问题

I'd like to select posts that have one or more comments using Rails 3 and a single query.

I'm trying something like this:

Post.includes(:comments).where('count(comments.id)>0')

However I get this error:

ActiveRecord::StatementInvalid: PGError: ERROR:  aggregates not allowed in WHERE clause

I've googled this and similar approaches, group by, etc with no luck. Any help will be appreciated.

回答1:

I'm sure you may have figured this out by now, but I believe what you're looking for is the having(:conditions) relationship, Jose.

Post.includes(:comments).having(:conditions => "count(comments.id) > 0")

I haven't tested that code so please take it with a grain of salt, but you should definitely be able to jump start from there.

来源：https://stackoverflow.com/questions/3980568/filter-by-count-of-children-using-rails-3