メモ。 singularize, constantize + send で処理を共通化できるかもしれない

call_class_name_by_string.rb

# 哀しみのドットつなぎテーブル名・カラム名が View か Controller か、どこからかやってくる
def search(table_and_column, search_values)
  # table_and_column : 'member_types.name'
  # search_values : %w[foo, bar]

  result =
    case table_and_column
    # New code
    when 'member_types.name' #, 'other_attr.name', 'some_attr.name'
      model_name =
        table_and_column.split('.') # => ['member_types', 'name']
                        .first # => 'member_types'
                        .singularize # => member_type
                        .split('_') # => ['member', 'type']
                        .map(&:camelize) # => ['Member', 'Type']
                        .join # => 'MemberType'
      user_column_name =
        table_and_column.split('.') # => ['member_types', 'name']
                        .first # => 'member_types'
                        .singularize # => 'member_type'

      # In Rails:
      ids =
        model_name.constantize.where('name IN (?)', search_values)
                              .map(&:id)
      # In Ruby:
      # ids =
      #   Kernel.const_get(model_name).where('name IN (?)', search_values)
      #                               .map(&:id)

      User.send("find_by_#{user_column_name}", ids)
    # Old codes
    when 'other_attr.name'
      # ...
      OtherAttr.where('name IN (?)', search_values)
      User.find_by_other_attr_id(ids)
    when 'some_attr.name'
      # ...
      SomeAttr.where('name IN (?)', search_values)
      User.find_by_some_attr_id(ids)
    end
  # and do something...
  #
  # attr_a = result.do_something
  # ...
end