Ruby on Rails nil cannot be forced in BigDecimal

Question

Why I get nil can't be coerced into BigDecimalwhen I try to do the calculation: here is the code:

model /drink.rb

class Drink < ActiveRecord::Base
  belongs_to :menu 
  before_save :total_amount 

def total_amount
    self.total_amount = self.price * self.quantity
end 

model /menu.rb

class Menu < ActiveRecord::Base
    has_many :drinks, :dependent => :destroy
    accepts_nested_attributes_for :drinks, :allow_destroy => true
    #Validations

end

* A drink is a (nested) child model and menu of the parent model. When I try to create a new drink, the browser displays an error messagenil can't be coerced into BigDecimal app/models/drink.rb:7:in 'total-amount' app/controllers/menus_controller.rb:47:in 'create' app/controllers/menus_controller.rb:46:in 'create'

Application / db / migration

class CreateDrinks < ActiveRecord::Migration
  def change
    create_table :drinks do |t|
      t.string :name
      t.decimal :quantity,:precision => 8, :scale => 2
      t.decimal :price, :precision => 8, :scale => 2
      t.decimal :vat, :precision => 8, :scale => 2
      t.references :menu

      t.timestamps
    end
    add_index :drinks, :menu_id
  end
end

Controllers / drinks _controller.rb

   class DrinksController < ApplicationController
      # GET /drinks
      # GET /drinks.json
      def index
        @drinks = Drink.all

        respond_to do |format|
          format.html # index.html.erb
          format.json { render :json => @drinks }
        end
      end

      # GET /drinks/1
      # GET /drinks/1.json
      def show
        @drink = Drink.find(params[:id])

        respond_to do |format|
          format.html # show.html.erb
          format.json { render :json => @drink }
        end
      end

      # GET /drinks/new
      # GET /drinks/new.json
      def new
        @drink = Drink.new

        respond_to do |format|
          format.html # new.html.erb
          format.json { render :json => @drink }
        end
      end

      # GET /drinks/1/edit
      def edit
        @drink = Drink.find(params[:id])
      end

      # POST /drinks
      # POST /drinks.json
      def create
        @article = Drink.new(params[:drink])

        respond_to do |format|
          if @drink.save
            format.html { redirect_to @drink, :notice => 'Drink was successfully created.' }
            format.json { render :json => @drink, :status => :created, :location => @article }
          else
            format.html { render :action => "new" }
            format.json { render :json => @drink.errors, :status => :unprocessable_entity }
          end
        end
      end

      # PUT /drinks/1
      # PUT /drinks/1.json
      def update
        @drink = Drink.find(params[:id])

        respond_to do |format|
          if @drink.update_attributes(params[:drink])
            format.html { redirect_to @drink, :notice => 'Drink was successfully updated.' }
            format.json { head :ok }
          else
            format.html { render :action => "edit" }
            format.json { render :json => @drink.errors, :status => :unprocessable_entity }
          end
        end
      end

      # DELETE /drinks/1
      # DELETE /drinks/1.json
      def destroy
        @drink = Drink.find(params[:id])
        @drink.destroy

        respond_to do |format|
          format.html { redirect_to drinks_url }
          format.json { head :ok }
        end
      end 
    end 

Please tell me what happened to the code?

Answer 1

If you want nil to be rated as 0.0, you can do something like this:

def total_amount
    self.total_amount = self.price.to_s.to_d * self.quantity.to_s.to_d
end 

Or explicitly check for nil

def total_amount
  if self.price && self.quantity
    self.total_amount = self.price * self.quantity
  else
    self.total_amount = "0.0".to_d
  end
end 

, , . , price quantity?

class Drink
  validates :price, :presence => true      # Don't forget add DB validations, too :)
  validates :quantity, :presence => true
end

, #total_amount .

Answer 2

quantity , nil nil .

, price decimal(n,2) ( n) , self.price Ruby BigDecimal; , BigDecimal.

irb :

>> 11 * nil
TypeError: nil can't be coerced into Fixnum
    from (irb):7:in `*'

self.price. , :

NoMethodError: undefined method `*' for nil:NilClass

,

validates_presence_of :quantity, :price

(, , ) , , .