Rails and select

In a rails project I’m working on, I was trying to select from the database some sales with some conditions.

Here is the Sale model:

class Sale < ActiveRecord::Base
  belongs_to :voucher
  belongs_to :client
  has_many :line_items, dependent: :destroy
  has_many :bills
end

So the goal of the task was to obtain all the Sales where the LineItems has express_checkout set it to true.

I thought it was easy. This is my initial code:

Sales.all.select do |sale|
  sale.line_items.select do |line_item|
    line_item.express_checkout == true
  end
end

So I saw this code and thought that must be right, but I kept getting all the Sales.

A friend told me to extract a method for this kind of check into the Sales' model, so I tried it and created a new method called express_checkout?`.

def express_checkout?
  l = line_items.select{|line_item| line_item.express_checkout == true}
  l.any?
end

This method did the same, but instead, I stored the result of the select result in a variable and then checked if there were any objects inside that variable. That approach worked.

So I thought select always returns an array with the elements that passed from the condition, but I didn’t know we have to store them in a variable and then check it.

The final code:

Sales.all.select do |sale|
  sale.express_checkout?
end