Sort Records by Total Number of Associations in Rails

Needed to be able to sort an index of records by the total number of has_many associations that existed on the record.

I originally wrote this scope:

class Carrier < ApplicationRecord
    has_many :loads, through: :dispatches

    scope :by_total_loads, -> {joins(:loads).group(:id).order('COUNT(loads.id) DESC')}
end

However, this would only return the Carriers with 1 or more associations.

Then, in Rails 5, left outer joins was introduced. A left outer join gets all the rows from the tables where the join conditions are met, while also leaving in the unmatched rows. That way, we could sort the index by number of total associations, and leave the 0 association records at the end!

Left Outer Joins in Rails 5

scope :by_total_loads, -> {left_joins(:loads).group(:id).order('COUNT(loads.id) DESC')}

I totally abstracted this, but this article was very helpful in understanding. https://www.ananunesdasilva.com/posts/understanding-activerecord-left-outer-joins