更新Rails数据库中的所有记录

Question

I am making an app in which users place bets on future scenarios like "Who Will Win American Idol?"

The user places his bet (referred to in the code as a prop).

Then later, the admin chooses the correct answer by editing the answer of the bet.

I want then, to check in the database to see whether the answer that each user has matches the answer that the admin has just provided.

I am trying to do something like this

  def update
    @user = User.find(session[:user_id])

    @prop = Prop.find(params[:id])
    @answer = Answer.find(params[:id])

    @prop.update(prop_params)

    User.all.map 
     { |user|
      #the code here is called once for each user
      # user is accessible by 'user' variable


      if @answer.choice == @prop.choice
        puts "hello"
        @user.score += 7
        @user.save
      else
        @user.score -= 7
        @user.save

      end
     }

  end

What is the best way to accomplish my goal?

Answer 1

It should be simply like this:

def update
  @user = User.find(session[:user_id])
  @prop = Prop.find(params[:id])
  @answer = Answer.find(params[:id])

  @prop.update(prop_params)
  score_change = @answer.choice == @prop.choice ? 7 : -7
  User.update_all("score = score + #{score_change}")
end

Explanation

This will return 7 or -7 as you want

score_change = @answer.choice == @prop.choice ? 7 : -7

Then we just update all user in a single query, don't need to iterate over each of user

User.update_all("score = score + #{score_change}")

Under the hook, this sql will be generated:

UPDATE "users" SET score = score + 7

Or

UPDATE "users" SET score = score + -7