SQL Query converting to Rails Active Record Query Interface

Question

I have been using sql queries in my rails code which needs to be transitioned to Active Record Query. I haven't used Active Record before so i tried going through http://guides.rubyonrails.org/active_record_querying.html to get the proper syntax to be able to switch to this method of getting the data. I am able to convert the simple queries into this format but there are other complex queries like

SELECT b.owner, 
       Sum(a.idle_total), 
       Sum(a.idle_monthly_usage) 
FROM   market_place_idle_hosts_summaries a, 
       (SELECT DISTINCT owner, 
                        hostclass, 
                        week_number 
        FROM   market_place_idle_hosts_details 
        WHERE  week_number = '#{week_num}' 
               AND Year(updated_at) = '#{year_num}') b 
WHERE  a.hostclass = b.hostclass 
       AND a.week_number = b.week_number 
       AND Year(updated_at) = '#{year_num}' 
GROUP  BY b.owner 
ORDER  BY Sum(a.idle_monthly_usage) DESC 

which i need in Active Record format but because of the complexity I am stuck as to how to proceed with the conversion.

The output of the query is something like this

+----------+-------------------+---------------------------+
| owner    | sum(a.idle_total) | sum(a.idle_monthly_usage) |
+----------+-------------------+---------------------------+
| abc      |               485 |         90387.13690185547 |
| xyz      |               815 |         66242.01857376099 |
| qwe      |               122 |        11730.609939575195 |
| asd      |                80 |         9543.170425415039 |
| zxc      |                87 |         8027.090087890625 |
| dfg      |                67 |         7303.070011138916 |
| wqer     |                76 |         5234.969814300537 |

Answer 1

Instead of converting it to an active record, you can use the find_by_sql method. Since your query is a bit complex.

You can use also use ActiveRecord::Base.connection, directly to fetch the records.

like this,

ActiveRecord::Base.connection.execute("your query") 

Answer 2

You can create the subquery apart with ActiveRecord and convert it to sql using to_sql

Then use joins to join your table a with the b one, that it is the subquery. Note also the use of the active record clauses select, where, group and order that are basically what you need to build this complex SQL query in ActiveRecord.

Something similar to the following will work:

subquery = SubModel.select("DISTINCT ... ").where(" ... ").to_sql

Model.select("b.owner, ... ")
  .joins("JOIN (#{subquery}) b ON a.hostclass = b.hostclass")
  .where(" ... ")
  .group("b.owner")
  .order("Sum(a.idle_monthly_usage) DESC")