return inside a block can replace a method’s own result and skip later code, which can break Rails helpers like capture and lose html_safe? information.

Calling instance_eval or instance_exec on a Rails 2 scope loads its records from the database. The issue is fixed in Rails 3+.

Rails session hashes can ignore merge!, leaving new values invisible or unsaved. update loads the session for writing and avoids the mismatch.

MiniTest deprecation warnings in Rails 4 often come from older test gems using the outdated API; adding minitest can silence one warning, but some require gem updates.

Ruby 1.9 triggers UTF-8 regexp warnings in Rails 2.3.16+ from ActiveSupport; a monkey patch in config/initializers suppresses them.

Rails select helpers can disable specific options by value, preventing choice of unavailable entries in forms.

link_to and content_tag accept a :data hash for HTML5 data attributes in Rails 3, simplifying data-foo and data-bam output.

console-for opens a remote Rails console on a Capistrano deployment target with one command, so staging and other environments can be accessed quickly.

Ruby has a reverse of Rails' each(&:method) shorthand for calling an object method with each element: each(&object.method(:call)).

Inspecting the generated Ruby for erb or haml templates helps debug rendering issues and understand what Rails executes. lookup_context.find_template and the template handler return the compiled output code.

Missing PostgreSQL types and query helpers for Rails 4.x make native array, CTE, and network-style filtering easier in ActiveRecord and Arel.

Google Analytics should run only in production to avoid polluting visitor statistics. Rails environment checks can gate the tracking snippet.

rake notes can miss TODOs in Haml, Sass, and CoffeeScript files unless Rails is taught their comment syntax and extensions.

Two high-severity Ruby on Rails security bugs and a rubygems.org compromise raise remote code execution risk for startups depending on the framework.

ANSI color codes in Rails logs clutter less and vim; stripping escape sequences with sed produces readable log output or a colorless file.

Enable the Ruby debugger in script/console or script/server to inspect methods and local variables during a Rails session.

Vendoring a patched Ruby gem in Rails can fail without gem metadata, especially with Bundler. A proper .specification file and :path setup make the local copy usable.

Expose controller logic to views so helper-style methods can be called from templates, with different APIs in Rails 2 and Rails 3+.

Large SQL queries become hard to maintain as joins, subqueries, and filters pile up. PostgreSQL views and materialized views can encapsulate that complexity in Ruby on Rails.

Need form builder helpers without emitting a surrounding <form> tag, for partial updates such as XHR-driven field changes. Rails fields_for yields the same builder without hidden inputs or authenticity token.

Passenger can start a Rails app in the wrong environment unless Apache is configured with the correct RailsEnv or RackEnv setting.

Rails 3 dbconsole misreads -p test and opens the development database unless the environment is passed first.