Module: ActiveRecord::ConnectionAdapters

# File 'activerecord/lib/active_record/connection_adapters.rb', line 26

def resolve(adapter_name) # :nodoc:
  # Require the adapter itself and give useful feedback about
  #   1. Missing adapter gems.
  #   2. Incorrectly registered adapters.
  #   3. Adapter gems' missing dependencies.
  class_name, path_to_adapter = @adapters[adapter_name.to_s]

  unless class_name
    raise AdapterNotFound, <<~MSG.squish
      Database configuration specifies nonexistent '#{adapter_name}' adapter.
      Available adapters are: #{@adapters.keys.sort.join(", ")}.
      Ensure that the adapter is spelled correctly in config/database.yml and that you've added the necessary
      adapter gem to your Gemfile if it's not in the list of available adapters.
    MSG
  end

  unless Object.const_defined?(class_name)
    begin
      require path_to_adapter
    rescue LoadError => error
      # We couldn't require the adapter itself.
      if error.path == path_to_adapter
        # We can assume here that a non-builtin adapter was specified and the path
        # registered by the adapter gem is incorrect.
        raise LoadError, "Error loading the '#{adapter_name}' Active Record adapter. Ensure that the path registered by the adapter gem is correct. #{error.message}", error.backtrace
      else
        # Bubbled up from the adapter require. Prefix the exception message
        # with some guidance about how to address it and reraise.
        raise LoadError, "Error loading the '#{adapter_name}' Active Record adapter. Missing a gem it depends on? #{error.message}", error.backtrace
      end
    end
  end

  begin
    Object.const_get(class_name)
  rescue NameError => error
    raise AdapterNotFound, "Could not load the #{class_name} Active Record adapter (#{error.message})."
  end
end