I have Bouquet and Flower objects:

class Bouquet < ApplicationRecord
  has_many :flowers
end

class Flower < ApplicationRecord
  belongs_to :bouquet

  enum color: {
    blue: 0,
    red: 1,
    yellow: 2,
    white: 3
  }
end

where a Bouquet will always have exactly one blue flower, one red flower, one yellow flower, and one white flower.

Suppose I have a page where I want to list all bouquets and their flowers in order, how can I query the flowers to minimize page load time?

In view (note that the white flower shows different info than the rest):

<% Bouquet.some_scope.each do |bouquet| %>
  <ul>
    <li><%= bouquet.name %></li>
    <li><%= bouquet.blue_flower.name %></li>
    <li><%= bouquet.red_flower.name %></li>
    <li><%= bouquet.yellow_flower.name %></li>
    <li><%= bouquet.white_flower.name_and_type %></li>
  </ul>
<% end %>

1. I've tried setting up the Bouquet model as follows:

class Bouquet < ApplicationRecord
  has_many :flowers

  def blue_flower
    flowers.find_by(color: :blue)
  end

  def red_flower
    flowers.find_by(color: :red)
  end

  # etc...

end

Then in the view: <% Bouquet.some_scope.includes(:flowers).each do |bouquet| %>

But all the find_bys ignore the includes and query the database for each flower.

2. Since the flowers (should) always be created in order, I've also tried

class Bouquet < ApplicationRecord
  has_many :flowers

  def blue_flower
    flowers.first
  end

  def red_flower
    flowers.second
  end

  # etc...

end

which works, but is it the best way of handling this?

CodePudding user response：

Since the flowers (should) always be created in order, I've also tried

SQL has no inherent order. If you want an order, you must provide it. You could flowers.order(:color) and then select off the list assuming that #1 is blue, #2 is red, etc... but that's fragile. What if you add more colors?

Since there's only four flowers, turn them into a Hash keyed on the color.

class Bouquet < ApplicationRecord
  has_many :flowers

  def flower_by_color(color)
    flowers_by_color[color.to_s]
  end

  private def flowers_by_color
    @flowers_by_color ||= flowers.index_by { |flower| f.color }
  end
end

Rather than hard coding the colors, use Flower.colors to loop through all the colors. Then if you add more Flower colors it will still work.

<% Bouquet.some_scope.includes(:flowers).each do |bouquet| -%>
  <ul>
    <li><%= bouquet.name %></li>
    <% Flower.colors.sort.each do |color| -%>
    <li><%= bouquet.flower_by_color(color).name %></li>
    <% end -%>
  </ul>
<% end -%>