ActiveRecord::RecordNotFound

ActiveRecord::RecordNotFound is raised when using find(), find_by!(), or first!/last! methods with an ID or conditions that match no records in the database.

Common causes

• Using find() with non-existent ID
• Record was deleted but still referenced
• URL manipulation with invalid IDs
• Stale data in cache or session
• Race condition where record is deleted mid-request

How to fix it

• Use find_by() which returns nil instead of raising
• Rescue the exception and show 404 page
• Validate record existence before operations
• Use where().first for optional records
• Implement proper 404 handling in controller

Example

# Error example
User.find(999)  # => ActiveRecord::RecordNotFound

# Fix with find_by (returns nil)
user = User.find_by(id: 999)
if user
  # process user
else
  # handle missing user
end

# Controller rescue
class UsersController < ApplicationController
  rescue_from ActiveRecord::RecordNotFound, with: :not_found

  private
  def not_found
    render file: 'public/404.html', status: :not_found
  end
end

Related errors