Ruby on Rails ActiveRecord Validations Using :on option
Example
The :on option lets you specify when the validation should happen.
The default behavior for all the built-in validation helpers is to be run on save (both when you're creating a new record and when you're updating it).
class Person < ApplicationRecord
# it will be possible to update email with a duplicated value
validates :email, uniqueness: true, on: :create
# it will be possible to create the record with a non-numerical age
validates :age, numericality: true, on: :update
# the default (validates on both create and update)
validates :name, presence: true
end
