CODEWITHSUNDEEP
ruby-on-railsdatabaseloopsselect
reesaspieces
reesaspieces

Reputation: 1810

Is it better to use select or loop through an array of records in Rails?

My goal is to write the query below in the cleanest, most efficient way possible and minimize hitting the DB. Appreciate any guidance in advance.

I have retrieved some records that belong to a user, like below:

english_shows = @user.shows.where(language: 'english')

Let's say the shows belong to different categories (using a foreign key), so it looks like below:

<ActiveRecord::Relation [
  <Show id: 1, category_id: 1, title: 'Rick and Morty'>,
  <Show id: 2, category_id: 2, title: 'Black Mirror'>,
  <Show id: 3, category_id: 3, title: 'Stranger Things'>,
  <Show id: 4, category_id: 3, title: 'Game of Thrones'>,
  ...
]

If I want to get the titles of the shows for each category, I know I can use select like this. The same thing can be done with where, but this would cause an additional DB call. ([Edit] Actually, both would hit the DB twice).

# Using select
cartoons = english_shows.select { |show| show.category_id == Category.find_by(name: 'cartoon').id}.pluck(:title)

# Using where
cartoons = english_shows.where(category_id: Category.find_by(name: 'cartoon').id)pluck(:title)

However, the select method would still result in multiple lines of long code (in my actual use case I have more category types). Is it cleaner to loop through the records like this (taken from this SO answer)?

cartoons, science_fiction, fantasy = [], [], []
@cartoon_id = Category.find_by(name: 'cartoon')
@science_fiction_id = Category.find_by(name: 'cartoon')
@fantasy_id = Category.find_by(name: 'cartoon')

english_shows.each do |show|
  cartoons << show if show.category_id == @cartoon_id
  science_fiction << show if show.category_id == @science_fiction_id
  fantasy << show if show.category_id == @fantasy_id
end

Upvotes: 0

Views: 1172

Answers (1)

nikamanish
nikamanish

Reputation: 772

Try this:

english_shows
  .joins(:category)
  .select('shows.*, categories.name as category')
  .group_by(&:category)

Upvotes: 3

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