Arel subselects with ActiveRecord? - mysql

Question

I'm using a slightly-modified version of the geocoded gem which returns this query when I call near on my model (calling Deal.near(southwest), where southwest is an array of geo coordinates):
SELECT
deals.*,
3958.755864232 * 2 * ASIN(SQRT(POWER(SIN((37.772476604436974 - addresses.lat) * PI() / 180 / 2), 2) + COS(37.772476604436974 * PI() / 180) * COS(addresses.lat * PI() / 180) * POWER(SIN((-122.42336332798004 - addresses.lng) * PI() / 180 / 2), 2) )) AS distance,
CAST(DEGREES(ATAN2( RADIANS(addresses.lng - -122.42336332798004), RADIANS(addresses.lat - 37.772476604436974))) + 360 AS decimal) % 360 AS bearing
FROM "deals"
INNER JOIN "companies" ON "companies"."id" = "deals"."company_id"
INNER JOIN "addresses" ON "addresses"."addressable_id" = "companies"."id" AND "addresses"."addressable_type" = 'Company'
WHERE (
addresses.lat BETWEEN 37.483013038215276 AND 38.06194017065867
AND addresses.lng BETWEEN -122.78956461309022 AND -122.05716204286986
)
GROUP BY
deals.id,
deals.created_at,
deals.updated_at,
deals.active,
deals.company_id,
deals.title,
deals.limitations,
deals.redemption_count,
addresses.lat,
addresses.lng
HAVING 3958.755864232 * 2 * ASIN(SQRT(POWER(SIN((37.772476604436974 - addresses.lat) * PI() / 180 / 2), 2) + COS(37.772476604436974 * PI() / 180) * COS(addresses.lat * PI() / 180) * POWER(SIN((-122.42336332798004 - addresses.lng) * PI() / 180 / 2), 2) )) <= 20
ORDER BY 3958.755864232 * 2 * ASIN(SQRT(POWER(SIN((37.772476604436974 - addresses.lat) * PI() / 180 / 2), 2) + COS(37.772476604436974 * PI() / 180) * COS(addresses.lat * PI() / 180) * POWER(SIN((-122.42336332798004 - addresses.lng) * PI() / 180 / 2), 2) )) ASC
My issue is that this will return multiple Deal records if that Deal's company has multiple Addresses, which I don't want.
In MySQL, I could just omit address.lat, address.lng in the GROUP_BY clause and it will properly group the records, but I can't do this in PostgreSQL.
I know I could wrap the whole query above in another SELECT and GROUP_BY, like this:
SELECT
id, created_at, updated_at, active, title, punches_to_complete, company_id, description, lat, lng, MIN(distance), bearing
FROM ( ... ) AS t
GROUP BY company_id
... where the ellipsis is the query from above. That (I believe) should get me the desired result in both MySQL and PostgreSQL.
The only problem is that I have no idea how to write this in ARel!
I had tried the following, a la this tip from the ARel guru, but I couldn't really make it work quite right (calling to_sql as the OP had said fixed his issue escapes the quotes, which freaks PostgreSQL out).
Can anyone help me with this???
UPDATE:
I've managed to get this done with an additional scope, like so:
scope :nearest, lambda { |coords|
subquery = "(#{Deal.near(coords).to_sql}) AS t1"
columns = Deal.columns.map{ |c| c.name }.join(',')
Deal.select(columns)
.select('MIN(distance) AS distance')
.from(subquery)
.group(columns)
.order('distance ASC')
}
However, this totally breaks chainability, as now I cannot call something like current_user.deals.nearest(coords), since that tags on an additional WHERE deals.user_id = 1 to the query outside of the subselect. I tried compensating for this by moving this logic into a class method and blanking the wheres clause on the SelectManager manually, like this:
def self.nearest(coords)
subquery = "(#{Deal.near(coords).to_sql}) AS t1"
columns = Deal.columns.map{ |c| c.name }.join(',')
query = Deal.select(columns)
.select('MIN(distance) AS distance')
.from(subquery)
.group(columns)
.order('distance ASC')
query.arel.ast.cores[0].wheres = []
query
end
... but that doesn't seem to work either: the additional WHERE clause is still appended:
Failure/Error:
#user.deals.nearest(southwest).first.distance.to_f.round(2).should ==
ActiveRecord::StatementInvalid:
Mysql2::Error: Unknown column 'deals.user_id' in 'where
clause': SELECT id,created_at,updated_at,user_id,company_id,
MIN(distance) AS distance FROM (SELECT deals.*, 3958.755864232 * 2 *
ASIN(SQRT(POWER(SIN((37.772476604436974 - addresses.lat) * PI() / 180
/ 2), 2) + COS(37.772476604436974 * PI() / 180) * COS(addresses.lat *
PI() / 180) * POWER(SIN((-122.42336332798004 - addresses.lng) * PI() /
180 / 2), 2) )) AS distance, CAST(DEGREES(ATAN2( RADIANS(addresses.lng
- -122.42336332798004), RADIANS(addresses.lat - 37.772476604436974)))
+ 360 AS decimal) % 360 AS bearing FROM deals INNER JOIN companies
ON companies.id = deals.company_id INNER JOIN addresses ON
addresses.addressable_id = companies.id AND
addresses.addressable_type = 'Company' WHERE deals.user_id =
26 AND (addresses.lat BETWEEN 37.483013038215276 AND 38.06194017065867
AND addresses.lng BETWEEN -122.78956461309022 AND -122.05716204286986)
GROUP BY
deals.id,deals.created_at,deals.updated_at,deals.user_id,deals.company_id,
addresses.lat, addresses.lng HAVING 3958.755864232 * 2 *
ASIN(SQRT(POWER(SIN((37.772476604436974 - addresses.lat) * PI() / 180
/ 2), 2) + COS(37.772476604436974 * PI() / 180) * COS(addresses.lat *
PI() / 180) * POWER(SIN((-122.42336332798004 - addresses.lng) * PI() /
180 / 2), 2) )) <= 20 ORDER BY 3958.755864232 * 2 *
ASIN(SQRT(POWER(SIN((37.772476604436974 - addresses.lat) * PI() / 180
/ 2), 2) + COS(37.772476604436974 * PI() / 180) * COS(addresses.lat *
PI() / 180) * POWER(SIN((-122.42336332798004 - addresses.lng) * PI() /
180 / 2), 2) )) ASC) AS t1 WHERE deals.user_id = 26 GROUP BY
id,created_at,updated_at,user_id,company_id ORDER BY distance ASC
LIMIT 1
Is what I'm trying to do even possible with ARel? The additional scopes above feel really dirty to me (parsing the subquery to raw SQL? I thought ARel was supposed to make it so I never did that!)
Related question: Can ARel formulate cross-db queries for CTEs (Common Table Expressions)?