If you only want to run a validation on an attribute if it is valid at that
point in the validation process then here's a trick:
module AttributeValidation
extend ActiveSupport::Concern
included do
attribute_method_suffix '_valid?', '_invalid?'
end
private
def attribute_valid?(attr)
!attribute_invalid?(attr)
end
def attribute_invalid?(attr)
errors.include?(attr.to_sym)
end
end
include this module in AR::Base or specific models - it's up to you. Once
included you can then set up your validations like this:
class User < ActiveRecord::Base
include AttributeValidation
attr_accessible :name, :age
validates :name, presence: true, length: { maximum: 100 }
validates :age, presence: true, numericality: { only_integer: true }
validate :over_minimum_age, if: :age_valid?
def over_minimum_age
errors.add(:age, :invalid) if age < 16
end
end
this will only run the minimum age validation once it has passed the presence
and numericality checks. One advantage of doing this is you don't need guard
checks when comparing the age (normally you'd get a "NoMethodError: undefined
method `<' for nil:NilClass")
Andrew
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