评等模型的average_rating列

Question

因此，我正在创建一个评级(明星)模型：

  create_table "posts", force: true do |t|
    t.string   "title"
    t.text     "content"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.integer  "user_id"
    t.integer  "total_stars",   default: 0, null: false
    t.integer  "average_stars", default: 0, null: false
  end

  create_table "stars", force: true do |t|
    t.integer  "starable_id"
    t.string   "starable_type"
    t.integer  "user_id"
    t.integer  "number"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

所以我已经知道如何得到总恒星：

star.rb:

  def add_to_total_stars
    if [Post].include?(starable.class)
      self.starable.update_column(:total_stars, starable.total_stars + self.number)
    end
  end

但是对于普通的恒星来说：

  def calculate_average_stars
    if [Post].include?(starable.class)
      self.starable.update_column(:average_stars, [SOMETHING MISSING HERE])
    end
  end 

我有点问题。

我想我必须创建一个列来存储文章中的所有numbers，这样我就可以这样做了：

2 + 4 + 2 / total_stars

编辑：

好吧，我试过这个：

  def calculate_average_stars
    if [Post].include?(starable.class)
      stars_list = self.starable.stars.map { |t| stars_list = t.number }   
      self.starable.update_column(:average_stars, stars_list.inject{ |sum, el| sum + el }.to_f / stars_list.size)
    end
  end

但我知道这个错误：

1.9.3-p0 :010 > star5.save
   (0.6ms)  begin transaction
  SQL (1.0ms)  UPDATE "posts" SET "total_stars" = 4 WHERE "posts"."id" = 5
  SQL (0.8ms)  UPDATE "posts" SET "average_stars" = NaN WHERE "posts"."id" = 5
SQLite3::SQLException: no such column: NaN: UPDATE "posts" SET "average_stars" = NaN WHERE "posts"."id" = 5
   (0.6ms)  rollback transaction
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: NaN: UPDATE "posts" SET "average_stars" = NaN WHERE "posts"."id" = 5

关于如何创建这样的表格，有什么建议吗？

Answer 1

你知道，如果你已经有了#total_stars，你就不能

def calculate_average_stars
  if [Post].include?(starable.class)
    self.starable.update_column(:average_stars, total_stars / stars.count)
  end
end 

-and更改posts表，以便average_stars可以成为浮点数而不是整数？