Rails migrations need path-specific logic for data updates while keeping rollback support. reversible, up_only, and reverting? handle direction-dependent SQL safely.

Marking code lines in RubyMine helps revisit complex spots quickly and keep your place with anonymous or mnemonic bookmarks.

Cookie expiry and HTTP cache lifetimes depend on the Date header when present; missing it can make mocked-time tests and browser caching behave inconsistently.

Custom RSpec matchers can stay local to one example group or selected groups, avoiding global helper pollution while reusing expectation logic.

Large refactorings risk breaking tests, blocking releases, and entangling unrelated changes; breaking work into small green steps keeps long-running project changes manageable.

Branch-based file links on GitHub and GitLab break when lines shift; commit- or tag-based URLs keep references stable.

Factories can make Ruby test suites slow by creating large association cascades and redundant records. TestProf helps identify factory hotspots with reports and flamegraphs.

Rails 7.1 changes fragment cache behavior, breaking Haml 5 buffer patches in apps that use caching. Upgrading to Haml 6 is needed for Rails 7.1+ with fragment caching.

URL text fragments let browsers deep-link to specific visible text without IDs, enabling highlighted shared links to arbitrary content.

Custom Ruby objects can gain colored, multiline IRB output by defining pretty_print; pretty_inspect is a simpler fallback when pretty printing is not needed.

Rails apps can generate entity relationship diagrams to visualize model dependencies and export them as images or PDF. rails-erd also supports limiting the diagram to selected models.

RSpec and Cucumber expectations can emit clearer failure messages, making test failures easier to diagnose when matching conditions or subsets of data do not behave as expected.

COUNT queries can be unexpectedly slow in PostgreSQL; any? and none? check for presence or absence without scanning for a full count.

Capistrano 3’s doctor task checks Ruby, Rubygems and Bundler versions, installed Capistrano gems, config variables and server settings.

Rails 7 fragment caching gets #caching? and #uncacheable! to detect cache context and prevent accidental caching of helpers or partials that must stay dynamic.

Ruby's JIT compiler needs a YJIT-enabled build and explicit activation; Rails 7.2+ enables it after boot, usually making it active already.

A pre-push Git hook can block pushes when RuboCop finds style or linting issues, and cached runs are much faster after the first check.

PostgreSQL enums keep a defined sort order, unlike string-backed columns whose collation can produce surprising results. Ordered enum values make priority fields behave predictably.

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.

Zeitwerk can eager load a single subdirectory so descendant classes are available for iteration, while avoiding manual require of the parent file.

ruby-warning customizes Ruby warning handling, letting specific messages or paths be ignored, warnings turned into errors, backtraces attached, and duplicates removed.

CSS attribute selectors can target partial values, letting links, classes, and other attributes be styled by prefixes, suffixes, substrings, or whitespace-separated tokens.

Passing an array as separate arguments avoids treating the whole array as a single value; ES6 ... and ES5 apply spread elements into a function call.