Fix warning in Ch08 - Validate quantity of products

[notapatch]

Section: Validate quantity of products

The book code listing for the validator causes a warning in Rails 6.1. The suggested warning fix, method add, has worked since Rails 3.

app/validators/enough_products_validator.rb
class EnoughProductsValidator < ActiveModel::Validator
  def validate(record)
    record.placements.each do |placement|
      product = placement.product
      if placement.quantity > product.quantity
        # ****************************** << deprecated in 6.1 ********************
        record.errors[product.title.to_s] << "Is out of stock, just #{product.quantity} left"    
      end
    end
  end
end

This generates the following warning:

DEPRECATION WARNING: Calling `<<` to an ActiveModel::Errors message array in order to add an error is deprecated. 
Please call `ActiveModel::Errors#add` instead. 
(called from block in validate at ... market_place_api/app/validators/enough_products_validator.rb:6)

You can fix this by changing errors method << to add. Add has been available since 3.0 and is the suggested change in 6.1 so this change works with the current code and future proofs the book.

record.errors.add product.title,  "Is out of stock, just #{product.quantity} left"

[madeindjs]

Great! Thank you for correct this warning 👍