Local Rails development can serve both HTTP and HTTPS with Passenger standalone by enabling SSL and using a self-signed certificate.

Date.today and Date.tomorrow can return the same day when Rails has no configured time zone, causing date handling to drift between UTC and local time.

log_level :debug can expose sensitive user data in Rails production logs, especially in SQL queries. Use :info, avoid SQL logging, and ensure filtered attributes are applied.

Rails development and test environments often replace real 404s with the debug page, which can hide authorization failures in request specs.

Find out whether a Rails validation failed by checking ActiveModel::Errors types instead of messages, which is useful in tests and for validations with extra options.

Migration output can report progress while batch-updating records with announce and say_with_time in Rails 3.1+.

Large Rails projects often duplicate date and datetime format strings, causing inconsistent output; named formats in Time::DATE_FORMATS and Date::DATE_FORMATS reduce repetition.

Inspect Rails emails in a real mail app by exporting a Mail::Message to .eml and opening it, instead of relying only on browser previews.

Controllers can call view helpers in Rails 5+ through helpers, while older Rails versions use view_context to reach methods like link_to.

becomes casts an ActiveRecord record to a different STI class so Rails can treat it as another type, while both instances share the same attributes.

Production releases can be linked to Git history by tagging the deployed revision automatically with Capistrano.

Growing memory usage in Ruby and Rails can exhaust a process and cause crashes; ObjectSpace.count_objects helps identify leaking object types, and derailed_benchmarks can aid diagnosis.

Webpacker 4 and Babel 7 change config files, package names, asset paths, and polyfill imports when upgrading a Rails app from Webpack 3.

RSpec partial double verification blocks stubbing helper methods that come from Rails controllers; without_partial_double_verification or a spec config can disable it temporarily.

Route constraints prevent ActionView::MissingTemplate errors on wrong requests by returning 404s instead of reaching an unmatched format or template lookup.

Migrating a larger Rails app from Bootstrap 3 to 4 often breaks styles, components and helper gems; planning library upgrades and rebuilding variables reduces the pain.

Pass nested form data to a plain model reader such as home_page, without a real association. Works for singular references, with manual record construction and no deletion support.

ActiveJob concurrency checks can pass falsely with the :test adapter because blocked jobs still enqueue; using :solid_queue verifies real blocking behavior.

Local email capture for Rails development avoids lost test messages and lets sent mail be viewed in a browser via MailCatcher.

Rails 6.1 strict loading prevents lazy association loading and raises errors when unread associations are accessed, helping avoid n+1 queries.

Redirects in Rails use different default status codes in controllers and routes, and an unintended permanent redirect can affect browser behavior.

Unlogged PostgreSQL tables can speed up Rails test suites by skipping the write-ahead log, but they raise crash-related data loss risk and stay unsuitable for production.

External images in emails can fail in some clients; inline attachments with Rails and attachments.inline keep images visible, but turn messages into multipart emails and use content IDs.

MySQL query caching hides true database timings during profiling; disabling it and Rails per-request caching reveals actual query costs.