The Hidden Risks of Delegation and N+1 Queries in Rails
Delegation is a common pattern in Ruby on Rails, allowing one object to pass a method call to another object. However, when used without caution, delegation can inadvertently lead to performance issues, particularly N+1 query problems. This article explores the pitfalls of delegation in Rails and how it can conceal N+1 issues.
Understanding Delegation in Rails
Delegation in Rails is often used for object composition, where a method in one class calls a method on another object. Rails provides the delegate method to facilitate this pattern.
class Order < ApplicationRecord
belongs_to :customer
delegate :name, to: :customer, prefix: true
end
In this example, Order delegates the name method to the customer object, allowing you to call order.customer_name.
The N+1 Query Problem Hidden by Delegation
An N+1 query issue occurs when a piece of code executes a separate database query for each element in a collection, leading to a linear growth in the number of queries based on the number of elements. This is a common performance anti-pattern in Rails applications.
Delegation can mask N+1 problems because it abstracts away the details of how data is…