Fix ActiveRecord::RecordNotFound: Couldn't find User with 'id'=999 in Rails

This error occurs when ActiveRecord's find method is called with an ID that does not exist in the database. Rails raises RecordNotFound which renders a 404 in production but shows a stack trace in development. Fix it by rescuing the exception in the controller or using find_by with a nil check for custom error handling.

Reading the Stack Trace

Here's what each line means:

• Couldn't find User with 'id'=999: The database has no User record with id=999. This is typically caused by a stale link, deleted record, or invalid URL parameter.
• app/controllers/users_controller.rb:8:in `show': The show action at line 8 calls User.find(params[:id]) with an ID that does not exist.
• lib/action_controller/metal/rescue.rb:22:in `process_action': Rails rescue middleware can catch this exception if you configure rescue_from in the controller.

Common Causes

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
  end
end

# URL: /users/999 (bookmarked months ago, user was deleted since)
class UsersController < ApplicationController
  def show
    @user = User.find(params[:id]) # Raises RecordNotFound for deleted user
  end
end

The Fix

Add a rescue_from handler in ApplicationController that catches RecordNotFound and renders a proper 404 page. This handles the error gracefully across all controllers without modifying each action individually.

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
  end
end

class ApplicationController < ActionController::Base
  rescue_from ActiveRecord::RecordNotFound, with: :record_not_found

  private

  def record_not_found
    render file: Rails.public_path.join('404.html'), status: :not_found, layout: false
  end
end

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
  end
end

Testing the Fix

require 'rails_helper'

RSpec.describe UsersController, type: :controller do
  describe 'GET #show' do
    context 'when the user exists' do
      let(:user) { User.create!(name: 'Alice', email: 'alice@example.com') }

      it 'returns 200' do
        get :show, params: { id: user.id }
        expect(response).to have_http_status(:ok)
      end

      it 'assigns the user' do
        get :show, params: { id: user.id }
        expect(assigns(:user)).to eq(user)
      end
    end

    context 'when the user does not exist' do
      it 'returns 404' do
        get :show, params: { id: 999 }
        expect(response).to have_http_status(:not_found)
      end
    end
  end
end

Run your tests:

rspec

Pushing Through CI/CD

git checkout -b fix/record-not-found-handler,git add app/controllers/application_controller.rb spec/controllers/users_controller_spec.rb,git commit -m "fix: add global rescue_from for RecordNotFound to return 404",git push origin fix/record-not-found-handler

Your CI config should look something like this:

name: CI
on:
  pull_request:
    branches: [main]
jobs:
  test:
    runs-on: ubuntu-latest
    services:
      postgres:
        image: postgres:15
        env:
          POSTGRES_DB: test_db
          POSTGRES_USER: postgres
          POSTGRES_PASSWORD: postgres
        ports:
          - 5432:5432
        options: >-
          --health-cmd pg_isready
          --health-interval 10s
          --health-timeout 5s
          --health-retries 5
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-ruby@v1
        with:
          ruby-version: '3.2'
          bundler-cache: true
      - run: bundle exec rails db:create db:migrate
        env:
          DATABASE_URL: postgres://postgres:postgres@localhost:5432/test_db
          RAILS_ENV: test
      - run: bundle exec rspec
        env:
          DATABASE_URL: postgres://postgres:postgres@localhost:5432/test_db
          RAILS_ENV: test

The Full Manual Process: 18 Steps

Here's every step you just went through to fix this one bug:

1. Notice the error alert or see it in your monitoring tool
2. Open the error dashboard and read the stack trace
3. Identify the file and line number from the stack trace
4. Open your IDE and navigate to the file
5. Read the surrounding code to understand context
6. Reproduce the error locally
7. Identify the root cause
8. Write the fix
9. Run the test suite locally
10. Fix any failing tests
11. Write new tests covering the edge case
12. Run the full test suite again
13. Create a new git branch
14. Commit and push your changes
15. Open a pull request
16. Wait for code review
17. Merge and deploy to production
18. Monitor production to confirm the error is resolved

Total time: 30-60 minutes. For one bug.

gem install bugstack

require 'bugstack'

Bugstack.init(api_key: ENV['BUGSTACK_API_KEY'])

Deploying the Fix (Manual Path)

1. Run rspec locally to confirm 404 responses for missing records.
2. Open a pull request with the rescue_from handler.
3. Wait for CI checks to pass on the PR.
4. Have a teammate review and approve the PR.
5. Merge to main and verify the 404 page renders in staging.

Frequently Asked Questions