Trouble with a nested query in Ruby on Rails

Question

I have three models Field , Flight , and FieldBoundaryDetail . Field has many Flights and has one FieldBoundaryDetail

Basically, i want to get every Field and FieldBoundaryDetail with the last flight.

I have written it in SQL. For sorting and searching purposes, i need it to be a Rails ActiveRecordRelation but am having a hard time converting this to Rails.

SELECT *
FROM fields
LEFT JOIN (SELECT * 
           FROM (SELECT * 
                 FROM flights
                 ORDER BY event_date DESC) AS flight
           GROUP BY flight.field_id
          ) AS flight ON fields.id = flight.field_id
INNER JOIN field_boundary_details ON fields.id = field_boundary_details.field_id

Answer 1

As a simple answer, you can use find_by_sql with the query you have, slightly modified:

Fields.find_by_sql "SELECT fields.*
                    FROM fields
                    LEFT JOIN (SELECT * 
                               FROM (SELECT * 
                                     FROM flights
                                     ORDER BY event_date DESC) AS flight
                               GROUP BY flight.field_id
                              ) AS flight ON fields.id = flight.field_id
                    INNER JOIN field_boundary_details ON fields.id = field_boundary_details.field_id"

Answer 2

I have a solution, but it's not very elegant. Hopefully someone can give a better answer.

latest_flight_ids = Field.latest_flight_for_each_field.map {|flight| flight.id.to_s}.join(",")
Field.select("*").
     joins("LEFT JOIN flights on fields.id = flights.field_id").
     joins(:field_boundary_detail).
     where("flights.id IN(#{latest_flight_ids}) OR flights.id IS NULL")