Rails 6 Action Text provides a built-in WYSIWYG editor for rich text fields, with Trix hooks for custom toolbar buttons and attachment handling.

Local HTTPS for Puma development needs a trusted certificate and SSL binding so Rails runs on https://localhost:3000 without browser warnings.

Centering a floated element can fit content width when inline-block is unavailable. A CSS/SASS wrapper and Rails helper provide IE7+ support.

Migrating a Rails app from yarn to npm can reduce dependency complexity and avoids upgrading to Yarn 2.0. Matching package versions helps keep installs stable.

Rails collections often retain empty strings, nil, whitespace, empty arrays, hashes, and false values; compact_blank removes them from arrays and hashes in Rails 6.1+.

Accessing Rails path helpers from plain Ruby classes can be awkward, and including all route helpers risks method clashes. Delegating url_helpers exposes only the needed path methods.

ActiveSupport::BroadcastLogger sends one log message to multiple outputs, useful for writing Rails and Sidekiq logs to both STDOUT and files.

Rails 2.3 can return either HTML or JSON from one controller action, but render_to_string inside format.json may trigger ActionView::MissingTemplate.

Rails can map selected exceptions to non-500 responses and suppress error monitoring noise, such as returning 404 for missing records or denied access.

Conditional cron jobs in whenever can target only one Rails environment or Capistrano stage, avoiding unwanted tasks on other deployments.

A stuck Rails development server can keep port 3000 busy and trigger EADDRINUSE; lsof and kill -9 can force it down.

PostgreSQL range types store date and time intervals in one column and fit ActiveRecord casting, overlap queries, and exclusion constraints for booking data.

ActiveRecord relation helpers reduce object instantiation, simplify association traversal and preloading, and bridge Rails version differences with a unified API.

Scopes defined as class methods can drop earlier filters when they return self; use all to preserve chained conditions in Rails 2 and 5.

Rails models often need exactly one of several attributes filled in; built-in validations do not handle this XOR case cleanly. A custom ActiveModel::Validator can enforce blank-or-singleton presence with clear errors.

Rails-friendly Middleman setup for live reload, asset pipeline, i18n, environment-specific config, browser testing, and Capistrano deployment.

Animated GIF uploads can slow Rails workers and waste processing time; dropping all but the first frame with ImageMagick avoids resizing work.

MySQL can coordinate multiple Rails processes with a database-backed mutex when code must not run concurrently. It is for model-level synchronization, not record locking.

Retrieve all values from one ActiveRecord column without instantiating records; pluck, ids, and distinct return arrays efficiently, with collect_column for older Rails.

Rails 7+ validates dates, numbers and strings with ComparisonValidator for greater-than and less-than checks, replacing custom comparison code.

Rails deployments with Webpacker and Capistrano often need asset-path, manifest, and compile-time tweaks to avoid slow releases and unused compression output.

Unsafe ActiveRecord query methods can expose applications to SQL injection when raw SQL is built from untrusted input.

Rails response tests can parse bodies by MIME type with parsed_body, replacing manual JSON.parse(response.body) in many cases and enabling cleaner assertions.

BUNDLE_GEMFILE selects a nondefault Gemfile for Bundler, making it possible to work with multiple Gemfiles in one project and test against different Rails versions.