database.yml

<% require_relative File.expand_path("git_worktree", __dir__) %>

default: &default
  adapter: postgresql
  encoding: unicode
  pool: 20
  connect_timeout: 5
  checkout_timeout: 5

development:
  <<: *default
  database: myapp_development<%= GitWorktree.db_suffix %>

test:
  <<: *default
  database: myapp_test<%= GitWorktree.db_suffix %><%= ENV["TEST_ENV_NUMBER"] %>

production:
  <<: *default
  database: myapp_production

git_worktree.rb

# config/git_worktree.rb
module GitWorktree
  PROJECT_ROOT = File.expand_path("..", __dir__)

  def self.name
    git_path = File.join(PROJECT_ROOT, ".git")
    git_dir = nil

    if File.file?(git_path)
      contents = File.read(git_path, 1024)
      if contents && contents =~ /\Agitdir:\s*(.+)\s*\z/
        git_dir = Regexp.last_match(1).strip
      end
    elsif File.directory?(git_path)
      git_dir = git_path
    end

    return nil unless git_dir&.include?("/worktrees/")

    raw = git_dir.split("/worktrees/").last.split("/").first
    sanitized = raw.to_s.gsub(/[^a-zA-Z0-9_]/, "_").downcase
    sanitized.empty? ? nil : sanitized
  end

  def self.db_suffix
    worktree = name
    worktree ? "_#{worktree}" : ""
  end
end