Sending extra SQL queries when model uses joins, includes

[kapellan]

I'm trying to get adverts with attachments(advert has_many attachments). If I use query without pagination:

@adverts = Advert.where(category_id: params[:id]).includes(:attachments).references(:attachments)
I get result in single query.

SELECT adverts.id AS t0_r0, adverts.created_at AS t0_r1, adverts.updated_at AS t0_r2, adverts.category_id AS t0_r3, adverts.title AS t0_r4, adverts.body AS t0_r5, adverts.user_id AS t0_r6, adverts.visible AS t0_r7, adverts.attachments_count AS t0_r8, attachments.id AS t1_r0, attachments.image AS t1_r1, attachments.created_at AS t1_r2, attachments.updated_at AS t1_r3, attachments.advert_id AS t1_r4 FROM adverts LEFT OUTER JOIN attachments ON attachments.advert_id = adverts.id WHERE adverts.category_id = 1

It supposes if I use pagination - the result will be in two queries(one is adverts with attachments, second count of adverts). But I get three queries: with limit, with attachments, and count.

@adverts = Advert.where(category_id: params[:id]).includes(:attachments).references(:attachments).page(params[:page])

SELECT DISTINCT adverts.id FROM adverts LEFT OUTER JOIN attachments ON attachments.advert_id = adverts.id WHERE adverts.category_id = 1 LIMIT 10 OFFSET 0

SELECT adverts.id AS t0_r0, adverts.created_at AS t0_r1, adverts.updated_at AS t0_r2, adverts.category_id AS t0_r3, adverts.title AS t0_r4, adverts.body AS t0_r5, adverts.user_id AS t0_r6, adverts.visible AS t0_r7, adverts.attachments_count AS t0_r8, attachments.id AS t1_r0, attachments.image AS t1_r1, attachments.created_at AS t1_r2, attachments.updated_at AS t1_r3, attachments.advert_id AS t1_r4 FROM adverts LEFT OUTER JOIN attachments ON attachments.advert_id = adverts.id WHERE adverts.category_id = 1 AND adverts.id IN (130, 131, 132, 136, 144, 150, 151, 153, 155, 158)

SELECT COUNT(DISTINCT adverts.id) FROM adverts LEFT OUTER JOIN attachments ON attachments.advert_id = adverts.id WHERE adverts.category_id = 1

Is it possible to get rid of extra query?

[skalb]

I'm having a similar problem (on Rails 4.1.x), but it seems like a Rails issue with eager load combined with limit/offset.

If you do:

@adverts = Advert.where(category_id: params[:id]).includes(:attachments).references(:attachments).limit(50)

You might still get the extra queries.