Math with table row values on Ruby on Rails

Lets supose I have a User table, and on this table I have height, weight and result rows. In a form I input height and weight valu开发者_如何学Goes and want to multiply those two values and store on the resulta row on database. I was trying something like that

  def create
    @user = User.new(params[:user])
    @result = @user.height * @user.weight
    @user.result = @result

But its not working, what am i doing wrong?

I think it would be nicer to have the computation done on a before_save filter on the model. Using the first 2 answers, it should look like this:

users_controller.rb

def create
  @user = User.new(params[:user])
  if @user.save
    redirect_to @user
  else
    render :action => :new
  end
end

user.rb

before_save :compute_result

def compute_result
  result = height * weight
end

You'd better put this logic (multiply) into your model, write a method for :before_save

That's the Rails Way!

See this API documentation: http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html

Make sure that params[:user] has values for :height & :weight keys. If yes, then you should set the fields height & weight as attr_accessible like this:

user.rb

class User < ActiveRecord::Base
  attr_accessor :height, :weight
end

users_controller.rb

def create
    @user = User.new(params[:user])
    @result = @user.height * @user.weight
    @user.result = @result
    if @user.save
      redirect_to @user
    else
      render :action => :new
    end
end