Rails and select

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

To start the Sale model has multiples associations .

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

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

I thought it was easy, in the Sales controller I will get all the sales Sales.all do a select Sales.all.select that’s the easy part, inside the block is were I got lost, because I have access to sale not the lineitems associated to it, I started trying to fetch the lineitems and perform another select inside.

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

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

A friend of mine told to extract a method for this kinf of task in the Salesmodel, so I gave it a try, and created a new method call express_checkout?. This method did basically the same but instead I store the result of the select in a variable and then check if there where any object inside that variable. That approach worked.

So my thoughts were inside the select always will return an array with the elemnts 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:

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