Rails N+1 query detection with Bullet

11058 views

                  Rails.application.configure do
  # Bullet configuration
  config.after_initialize do
    Bullet.enable = true
    Bullet.alert = true # Show JavaScript alert
    Bullet.bullet_logger = true # Log to bullet.log
    Bullet.console = true # Show in browser console
    Bullet.rails_logger = true # Add to Rails log
    Bullet.add_footer = true # Add warning to HTML footer

    # Raise errors in tests
    Bullet.raise = true if Rails.env.test?
  end
end

                  # BAD - N+1 query (1 query for posts + N queries for authors)
def index
  @posts = Post.published.limit(20)

  render json: @posts.map do |post|
    {
      title: post.title,
      author_name: post.author.name # N queries!
    }
  end
end

                  # GOOD - Eager loading (2 queries total)
def index
  @posts = Post.published
               .includes(:author)
               .limit(20)

  render json: @posts.map do |post|
    {
      title: post.title,
      author_name: post.author.name # No additional queries
    }
  end
end

N+1 queries are the most common Rails performance problem—loading associations in loops causes exponential database queries. The Bullet gem detects N+1s in development and suggests fixes. It monitors queries and alerts when you should use includes, preload, or eager_load. I configure it to show notifications in the browser console and raise errors in tests. The gem also catches unused eager loading, where you preload associations but never access them. Fixing N+1s typically involves adding includes(:association) to queries. For complex nested associations, I use strict_loading mode to catch issues early. Bullet is essential tooling—it finds issues CI can't catch.

Maya Patel

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Rails N+1 query detection with Bullet

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