Access data from join-table in has_many :through, preventing additional data loading

Question

Rails 4.1.7

I have 3 models.

# Report
class Report < ActiveRecord::Base
  has_many :computed_values, dependent: :destroy
  has_many :settlements, through: :computed_values
end

# ComputedValue
class ComputedValue < ActiveRecord::Base
  belongs_to :report
  belongs_to :settlement
end

# Settlement
class Settlement < ActiveRecord::Base
  has_many :computed_values
  has_many :reports, through: :computed_values
end

ComputedValue has an attribute distance .

I want to get such construction works: Report.first.settlements.first.distance which is ComputedValue.find(report_id: Report.first.id, settlement_id: Report.first.settlements.first.id).distance

Is there any elegant and fast way to get that worked?

When I call Report.first.settlements.first , Rails has already loaded records for first report, first settlement and record from join-table computed_values . How to prevent second loading from computed_values for finding values and use data from already loaded records?

Answer 1

Ok, I found a solution.

# Report
has_many :settlements, -> {select("settlements.*, computed_values.distance AS distance")},
          through: :computed_values

After that, Report.first.settlements.first.distance works just perfectly!