You have probably heard of N+1 queries problem. In the rails community, there are a bullet and rspec-sqlimit gems that help to detect this kind of queries. sequel_query_limit is a Sequel extension that pursuits the very much similar goal as rspec-sqlimit does. Maybe a little more :)

PLEASE NOTE IT IS NOT READY BY ANY MEANS, SPECS ARE MISSING & ANALYSIS IS REALLY SUCKS ATM :D

First of all, we shall enable an extension as described in the sequel docs

require 'query_limit'
Sequel::Database.extension(:query_limit)

module SqlHelper
  def self.included(base)
    base.before(:each) { QueryLimit::Listener::Global.watch }
    base.after(:each)  { QueryLimit::Listener::Global.analyze(np1: true, reset: true) }
    base.after(:all)   { QueryLimit::Listener::Global.die }
  end
end

RSpec.configure do |config|
  config.include SqlHelper, watch_sql: true
end

RSpec.describe App::Companies::Serializer do
  subject { described_class.new(company).to_hash }

  let(:company) { Fabricate(:company) }

  it 'serializes company with its associations', :watch_sql do
    is_expected.to have_key :users
  end
end

If query_limit will catch up N+1 query it will print an SQL query with its backtrace to the STDOUT.

Using this technique you can check individual (or group of) examples for N+1 quries withouth wrapping everything into DB.with_query_limit block.

DB.with_query_limit(/SELECT/, max: 3) do
  collection = Models::Company.limit(10).all
  App::Companies::Serializer.for_collection.new(collection).to_hash
end

This will return result of your query if it's not exceeding specified max limit. Otherwise, it will raise an exception with captured sql queries.

May be useful for ad-hoc testing via console.

• Add configuration option for what to do when query exceeds a limit (raise exception or run a callback)
• Add configuration option for what to do when N+1 problem found
• Add RSpec matchers
• Add option to limit by query execution time
• Add ability to pass custom sql backrace formatter
• Add ability to analyze on the fly

Bug reports and pull requests are welcome!

The gem is available as open source under the terms of the MIT License.