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Ruby on Rails

Random notes:

  • attr_accessor creates a getter and setter
  • When using the mysql2 gem, for database connectivity, setting the host to localhost in config/database.yml will make Rails attempt to connect to MySQL or MariaDB over a socket rather than a TCP connection. Use a loopback IP instead.

Psych::BadAlias: Unknown alias error​

Scenario: when starting a Rails application up, a Psych::BadAlias: Unknown alias: <something> error shows up.

This can be caused by a few things:

  • Typos in your ‘config/database.yml’ file. Double check your aliases are specified correctly.

    default: &default
      adapter: mysql2
      pool: 5
      timeout: 5000
      encoding: utf8

    development: <<: *defaults # THIS IS A TYPO

  • If you are running Ruby >= 2.7.0, Rails >= 5, < 7, check Gemfile.lock for the psych gem. Psych 4.0 introduced a breaking change for aliases. Create an entry in Gemfile to keep Psych in 3.x.

    gem 'psych', '< 4'

Useful Gems​