Challenge 1: Validate a Model — Solution

class Product < ApplicationRecord
  validates :name, presence: true, length: { maximum: 50 }
  validates :price, numericality: { greater_than: 0 }
  validates :sku, uniqueness: true
end

product = Product.new(name: "", price: -5)
product.valid?
puts product.errors.full_messages

=begin
Expected output:
Name can't be blank
Price must be greater than 0

Notes:
- name: "" fails the presence: true validator, producing "Name can't be
  blank".
- price: -5 fails numericality: { greater_than: 0 }, producing "Price
  must be greater than 0".
- sku isn't set at all in this example, so its uniqueness validator
  isn't shown failing here — uniqueness only becomes relevant once a
  value exists to compare against other rows.
- .valid? runs every validator and returns false, populating errors as a
  side effect; .save would behave the same way, refusing to write to the
  database and returning false instead of raising an exception.
=end