Boring Rails

Tip: Pluck single values out of ActiveRecord models or Enumerables

:fire: Tiny Tips

Rails has a great, expressive term called pluck that allows you to grab a subset of data from a record. You can use this on ActiveRecord models to return one (or a few) columns.

But you can also use the same method on regular old Enumerables to pull out all values that respond to a given key.


In Rails, use pluck to query a subset of columns.
# SELECT "shoes.*" from "shoes"
# => ["Air Force 1", "NMD_2", "Air Jordans", ... ]
# This returns an array with all shoe names, but our database query pulled down all of the columns on the `shoes` table

# SELECT "" from "shoes"
# => ["Air Force 1", "NMD_2", "Air Jordans", ... ]
# Same result, but we only query exactly the columns we wanted

Shoe.pluck(:name, :brand)
# SELECT "shoes"."name", "shoes"."brand" FROM "shoes"
# => [["Air Jordan 1 Mid", "Nike"], ["Air Jordan 1 Mid", "Nike"], ... ]

# SELECT DISTINCT "shoes"."brand" FROM "shoes"
# => ["Nike", "Adidas", ... ]

You can also use pluck with Enumerables when using ActiveSupport:

  { id: 1, name: "David" },
  { id: 2, name: "Rafael" },
  { id: 3, name: "Aaron" }

# => [ "David", "Rafael", "Aaron" ]

I find the Enumerable version to be particularly handy when dealing with JSON data from external APIs.

require "httparty"
require "active_support"
require "active_support/core_ext"

response = HTTParty.get('')
questions = JSON.parse(response.body)["items"]

# => [
#   "JavaScript to Python - Interpreting JavasScript .filter() to a Python user",
#   "Nuxt generate and firebase gives timer warning",
#   "Variable expected error when I increment the value of a map",
#   ...
# ]

While pluck is most often used with Hashes, you can use it with any object that responds to the message you pass in – including regular Ruby objects or Structs.

Next time you find yourself calling map to get back a single value, see if your code might be improved by switching to pluck.

Additional Resources

Rails API Docs: ActiveRecord#pluck

Rails API Docs: Enumerable#pluck

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