joinした結果を全て取得するやつ

model.rb

class Model < ActiveRecord::Base
  scope :retrieve_all, ->(*tables) {
    select_stmt = [%{`#{self.table_name}`.*}]

    select_stmt << tables.map {|t|
      ar = ActiveRecord::Base.const_get(t.to_s.classify.singularize)
      table_name = ar.table_name
      table_name_single = table_name.singularize

      ar.attribute_names.map {|col|
        col == 'id' ? nil : %{`#{table_name}`.`#{col}` as `#{table_name_single}_#{col}`}
      }
    }
    joins(*tables).select(select_stmt.flatten.compact.join(","))
  }
end