Question

I have complex query that I want to join itself to do additional computations. In sql I can do

SELECT t1.*, t2.*
FROM (SQL) AS t1
INNER JOIN
(SQL) AS t2
ON t1.num = t2.num - 1

Suppose the SQL is the query I want to join.

How to do that in rails with ActiveRecord / arel (or something else) to get ActiveRecord::Relation and to be able to use where() on it.

If I do it with sql and execute/select_all I get PG:result or hash and can’t use where memthod anymore.

Answer 1

First solution is interpolating other query using to_sql method:

Place.select("places.*, communes.*").joins("INNER JOIN (#{
  Commune.where(:id => [1,2,3]).to_sql
}) as communes ON communes.id = places.commune_id")

Second solution is using Arel’s merge method:

Place.select("places.*, communes.*")
  .joins(:commune)
  .merge(Commune.where(:id => [1,2,3]))