Firefox 5.0.1 no longer runs on Ubuntu 14.04, so Selenium test setups need browser and gem updates to keep Rails 2.3 and Cucumber projects working.

Enable Rails-style autoloading in a plain Ruby setup by adding load paths to ActiveSupport::Dependencies.autoload_paths.

Targeted database migrations in Rails use STEP and VERSION to run, redo, rollback, or revert a chosen migration without processing the full history.

Passing untrusted parameters into url_for or _url helpers can create open redirect vulnerabilities and send users to attacker-controlled hosts.

Ace editor adds syntax highlighting and auto-indenting for in-browser code editing, with a working brace setup for Ruby on Rails Webpacker and Webpack 2.

Lightweight record filtering for Rails replaces FULLTEXT indexing with LIKE queries and keeps search compatible with MySQL and PostgreSQL.

Old cronjob management with craken no longer works on Rails 3.2+, so whenever becomes the replacement for deploying rake tasks into cron.

Rake tasks in lib/tasks are ignored when the filename ends in .rb; Rails and Rake load them only from .rake files.

ONLY_FULL_GROUP_BY in MySQL 5.7 rejects queries that select non-grouped columns, preventing nondeterministic results and breaking some Rails scopes.

A Bash function can route rake to bin/rake when Spring binstubs exist, otherwise to bundle exec rake, speeding Rails 4.1+ and avoiding version conflicts on older apps.

Rails automatically applies a same-named layout for a controller, which can create surprising view behavior when an unintended template is picked up.

PostgreSQL offers native column types such as json and arrays that simplify data modeling in Rails and can replace awkward workarounds from MySQL.

Virtual ActiveRecord attributes can lose Rails-style type casting, causing string values, validation roundtrip bugs, and broken select boxes. Virtus restores coercion for non-persistent fields.

Edge Rider adds utility methods and compatibility patches for working with ActiveRecord scopes across Rails versions, reducing breakage from changing scope APIs.

Path traversal probes in Rails request parameters can indicate attempts to exploit CVE-2019-5418. Fixed releases block the vulnerability.

Nested ActiveRecord transactions can hide inner ActiveRecord::Rollback exceptions or fire after_commit callbacks too early, depending on joinable: false and requires_new.

Rails 2.3 tests can fail with NoMethodError: undefined method 'cache' for Gem:Module when used with newer RubyGems; downgrading RubyGems restores generator lookup behavior.

Running Solr with Sunspot adds Rails search, but requires local setup, reindexing, error handling, and production configuration for a separate Solr server.

Rails console debugging for mail delivery failures, with ActionMailer settings inspection and a direct test message to verify SMTP and spam score.

Ruby 1.9 upgrades in Rails apps often fail because of gem incompatibilities, lambda arity issues, and encoding mismatches between files, strings, and databases.

Resque dashboard access can bypass ApplicationController filters in Rails 3, so a Rack middleware can protect it with Clearance and a remember token.

Travis CI builds can break after Ubuntu image changes, causing PostgreSQL, MySQL, and Rails test failures. Pinning dist: trusty keeps the older environment until the setup is updated.

Rails with recent Rack versions can emit a session cookie security warning when no secret is configured; locking Rack to 1.4.1 works around the issue.