Ruby on Rails inefficient database query - ruby-on-rails

Question

My Rails app has the following conditions:
Each Style has many Bookings
Each Booking has a single warehouse value, and a single netbooked value
I need to update the warehouse_netbooked column of every Style with a hash containing the total netbooked sum for each warehouse across all of the style's bookings.
My current code works, but is way too slow (each iteration is taking ~0.5s, and there are thousands of styles):
def assign_warehouse_bookings
warehouses = ["WH1","WH2","WH3"]
Style.all.each do |s|
style_warehouse_bookings = Hash.new
warehouses.each do |wh|
total_netbooked = s.bookings.where(warehouse: wh).sum(:netbooked)
style_warehouse_bookings[wh] = total_netbooked
end
s.update(warehouse_netbooked: "#{style_warehouse_bookings}")
end
end

Answer 1

Here a small change to your code to avoid to do many queries following #eric-duminil advise
#styles = Style.includes(:bookings)
#styles.each do |s|
style_warehouse_bookings = Hash.new
warehouses.each do |wh|
total_netbooked = s.bookings.map {|book| book.warehouse.eql?(wh) ? book.netbooked : 0}.sum
style_warehouse_bookings[wh] = total_netbooked
end
s.update(warehouse_netbooked: "#{style_warehouse_bookings}")
end
end
I hope it help you.

Answer 2

In your case, you have for a single style, you are fetching booking with 3 type of warehouses finding sum of netbooked for each type of warehouse. This is highly inefficient.
One good rule is, first fetch required data from database, and after fetching data use ruby to handle data. It's important to fetch only required data. So, in your case, you can fetch styles and all related bookings. Then you can iterate through collection of bookings and prepare style_warehouse_bookings hash.
use find_each instead of each
use includes or preload to preload data.
Here is simple example which will definitely improve performance,
warehouses = ["WH1","WH2","WH3"]
# preload bookings with style, `preload` used explicitely instead of `includes` to prevent cross join queries.
styles = Style.joins(:bookings).where('bookings.warehouse' => warehouses).preload(:bookings)
# find_each fetches data in batches of 1000 records
styles.find_each do |s|
style_warehouse_bookings = Hash.new
warehouses.each do |wh|
# select and sum methods of ruby are used instead of where and sum of active-record
total_netbooked = s.bookings.select{ |booking| booking.warehouse = wh }.sum(&:netbooked)
style_warehouse_bookings[wh] = total_netbooked
end
s.update(warehouse_netbooked: "#{style_warehouse_bookings}")
end
Read in depth about preload, includes and joins at eager loading associations documentation. Apart from that I wrote an article on when to use preload, includes and joins here which can help.

Answer 3

I think you want to do batch update. If I am correct check the following
link
Is there anything like batch update in Rails?
Also you can introduce transaction to avoid too many commits
For example
def assign_warehouse_bookings
Style.transaction do
<your remaining code goes here>
end
end