Forum: Ruby on Rails Should includes work with a query that returns the same object more than once?

436baafc7a070619f5dd6efa423b7d00?d=identicon&s=25 Dave Schweisguth (Guest)
on 2014-08-06 08:34
(Received via mailing list)
My app has models Person, Photo, Comment. A Comment has_many Photos and
a
Photo has_many People.

In the console, with a database with some data in it and the
ActiveRecord
logger sent to STDOUT ...

First, to show what's in the data:

irb(main):003:0> Photo.joins(:comments).order(:id).limit(2).map &:id
D, [2014-08-05T18:19:10.528376 #24027] DEBUG -- :   Photo Load (20.6ms)
SELECT  `photos`.* FROM `photos` INNER JOIN `comments` ON
`comments`.`photo_id` = `photos`.`id`  ORDER BY `photos`.`id` ASC LIMIT
2
=> [1, 1]

Photo.joins(:comments).order(:id).limit(2) returns the same photo twice,
because it has two comments. That's what I want. (This is cut down from
a
much larger query where this behavior is actually useful.) Now for the
problem:

irb(main):001:0>
Photo.joins(:comments).includes(:person).order(:id).limit(2).each { |f|
puts f.person.username }; nil
D, [2014-08-05T18:17:44.613676 #24027] DEBUG -- :   Photo Load (0.6ms)
SELECT  `photos`.* FROM `photos` INNER JOIN `comments` ON
`comments`.`photo_id` = `photos`.`id`  ORDER BY `photos`.`id` ASC LIMIT
2
D, [2014-08-05T18:17:44.811715 #24027] DEBUG -- :   Person Load (0.3ms)
SELECT `people`.* FROM `people`  WHERE `people`.`id` IN (1)
user1
D, [2014-08-05T18:17:44.845897 #24027] DEBUG -- :   Person Load (0.6ms)
SELECT  `people`.* FROM `people`  WHERE `people`.`id` = 1 LIMIT 1
user1

Even though I said includes(:person), and it did cause ActiveRecord to
issue the second query to get all the people, when I retrieve the second
Photo's Person ActiveRecord has to query it again. With a production
query
with many more photos and people it's very slow.

Is this a bug? Is includes not supported with a query that returns the
same
object more than once? Is there a way around the N + 1 queries?

Thanks!
D6db2458ee273bb0e67556224c7ddcff?d=identicon&s=25 Pardeep Dhingra (pardeep_d)
on 2014-08-07 13:57
@photos = Photo.includes(comments: :person).all
436baafc7a070619f5dd6efa423b7d00?d=identicon&s=25 Dave Schweisguth (Guest)
on 2014-08-07 15:09
(Received via mailing list)
On Thursday, August 7, 2014 4:58:21 AM UTC-7, Ruby-Forum.com User wrote:
>
> @photos = Photo.includes(comments: :person).all
>

Thanks, but that's not what I'm trying to do. Photo.joins(:comments)
returns a Photo for each Comment; if a Photo has two Comments I want it
to
appear twice in the query result. (That seems foolish but, as I said in
my
original post, this is cut down from a much larger query where this
behavior is actually useful.) What you suggest gives me only one of each
Photo regardless of its number of Comments. How can I get includes to
work
with my query (or another query with the same behavior), or can I?
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