Missing Eager Load (ARCH6051)

Key ruby.orm.missing-eager-load · Severity warning · Category orm

A query that iterates over related data without declaring eager loading is the root cause of N+1. In ActiveRecord the relation must be preloaded with includes/preload/eager_load.

Incorrect

def comment_authors
  Comment.recent.map { |c| c.user.email }  # user not eager-loaded
end

Correct

def comment_authors
  Comment.recent.includes(:user).map { |c| c.user.email }
end

Fix

Declare the relations accessed inside the loop with includes so they load in a single query.