Model has a attribute based on a query (N+1)

Question

I have the next model. It has an attribute base on a query. Because that attribute I have the N+1 problem when I show the record on my application.

Doing Dish.all.includes(:entries) will not work because this section from_today.from_current_time of the query.

class Dish < ApplicationRecord
  has_many :entries, dependent: :destroy

  belongs_to :user
  belongs_to :category

  before_validation :init, on: :create

  def available?
   current_entry = entries.from_today.from_current_time
   return false if current_entry.count.zero?
   current_entry.first.dishes_left.positive?
  end

end

Answer 1

You may add an association with an condition:

class Dish < ApplicationRecord
  has_many :entries
  has_many :entries_from_today,
    -> { merge(Entry.from_today) },
    class_name: 'Entry'

After that you may do like this:

dishes = Dish.all.includes(:entries_from_today)
dishes.each do |dish|
  puts dish.entries_from_today
end