Passing last_modified without an object skips ETag generation, so second-level timestamps can make distinct responses look identical and break cache-related tests.

Useful Rails rake tasks expose code statistics, comment tags, and environment details for quick project inspection.

Rails session and cookie lifetime defaults can be surprising, and Clearance authentication tokens expire separately. Changing expiry settings requires different configuration points or a patch to sign_in.

Always-on UI behaviors like polling, animations, autocomplete, and lazy loading can make E2E tests flaky; feature flags disable them by default and re-enable them only where needed.

Accessing the Rails session ID is only possible when a session ID exists; exposing it is risky and should be done carefully.

rake can fail with a misleading cannot remove Object::ClassMethods error when a hidden boot-time exception triggers Rails cleanup instead of the real cause.

Geordi 1.0 consolidates Rails project commands into a single CLI with command lookup, dependencies, and new setup, update, console, shell, and test workflows.

Rails SafeBuffer loses HTML safety after many string transformations, and in-place replacement can raise TypeError; this prevents injection tricks through user input.

Compute readable differences between two strings in Ruby or Rails with the differ gem, including word, line, and character comparisons plus HTML or color output.

Rails 5 model classes inherit from ApplicationRecord, making it the shared home for logic used by all application models instead of patching ActiveRecord::Base.

Rails applications can send mail through Gmail’s SMTP server with smtp_settings; Google app passwords enable delivery when two-factor authentication is enabled.

Upgrading Ubuntu from Ruby 1.8.7 to 1.9.2 can break Rails 2 apps using RSpec and removes installed gems, but Bundler can restore dependencies.

Rails asset delivery relies on manifests and explicit requires; precompilation output helps verify URLs and troubleshoot missing or misplaced assets.

Rails startup can fail with a NameError when version_requirements is missing on Rails::GemDependency; a small environment.rb patch restores compatibility with newer RubyGems.

Get the PostgreSQL server version from a Rails app or console using ActiveRecord::Base.connection.select_value('SELECT version()') when you need database details at runtime.

Use oj to generate JSON much faster for large Ruby hashes, but account for symbol handling, Rails compatibility, and HTML escaping to avoid XSS.

Rails or Rake can report missing gems even when they are installed; wrong Bundler configuration or release-directory leftovers often redirect gem lookup to the wrong place.

Runtime association filters are hard in Rails because :conditions cannot take a lambda; a string-interpolation hack or proc can evaluate date-based rules.

Legacy data can be imported into a new Rails app by connecting a second database and mapping old tables and columns with Active Record models.

Bot traffic can trigger ActionView::MissingTemplate by requesting bogus URL suffixes. Restricting allowed request formats application-wide prevents invalid format parameters from reaching controllers.

Rails XSS protection can escape ActionMailer email bodies unexpectedly. A configuration initializer prevents rails_xss from escaping mail content.

def_delegator and def_delegators are hard to read; delegate or a small wrapper method makes Rails delegation clearer.

Custom flash types let controllers use extra redirect messages such as success, useful for Bootstrap-style alerts beyond notice and alert.

Spring keeps bin/rails and bin/rspec fast, while parallel_tests can break shared test runs unless Spring is disabled in parallel contexts.