4 Mistakes to Avoid as a RoR Engineer

Ruby on Rails is a powerful framework that if used properly can speed up development and provide a strong foundation for a scalable application. However, some simple mistakes can quickly make Rails a burden.

Photo by Sarah Kilian on Unsplash

1. Forgetting to Check for N+1 Queries

N+1 occurs when a record collection is retrieved without loading its required associations. This leads to 1 query to fetch the original collection and N queries to fetch the association of each record. This causes a slowdown due to an unnecessarily large number of DB roundtrips. Instead, we should eager load the first query so we can make a single larger query (with the ID of all elements in association) to fetch the associated records. A great way to check for N+1 queries and get suggestions on how to fix them is the Bullet gem.

Model

class User < ApplicationRecord
  has_one :picture
end

Serializer

class UserSerializer < ApplicationSerializer
  identifier :id
  fields :name, :username, :created_at
  association :picture, blueprint: PictureSerializer
end

Controller

# WRONG
def index
  @users = User.all
  render json: UserSerializer.render(@users)
end
# CORRECT
def index
  @users = User.all.includes(:picture)
  render json: UserSerializer.render(@users)
end

For more on information on N+1 queries:

Eager Loading Polymorphic Associations in Ruby on Rails

2. Using Map Vs Pluck

Developers of other languages may use the iterator method map interchangeably with ActiveRecord specific methods such as pluck. However, the former runs once for each record in the association which requires the entire record set to be loaded in memory while the latter runs a query that returns the desired values directly.

# WRONG
MyModel.all.map(&:my_favorite_attribute)
# CORRECT
MyModel.all.pluck(:my_favorite_attribute)