Newbie seeking advice on DRYing up my model validations


Despite close reading of Matz’s Ruby book and Agile Web Dev. w. Rails,
I can’t figure out how to tackle the challenge of sharing validation
code across models with attributes in common.

In each of my models I’d like to validate the shared attributes with a
custom validator that includes Rails ActiveRecord::Validations class
methods and some of my own validations. My problem is 1) I don’t know
how to pass attribute references to my special method and 2) (mundane)
I can’t successfully call any ActiveRecord::Validations class methods
from within my custom method.

A bit of garbage here, I know, but any thoughts? Is this kind of
problem handled by use of certain gems?



Hi Grar,

If you have a User model where you want to use some shared validations,
could create a module like this – in lib/my_email_validations.rb:

module MyEmailValidations
def self.included(base)
base.validates_presence_of :email
base.validates_length_of :email, :minimum => 6
base.validate :email_must_be_from_valid_provider

# example of a custom validator
def email_must_be_from_valid_provider
  errors.add :email, "must be from a valid provider" if
    email !~ /$/


and in your User model, include them like this:

class User < ActiveRecord::Base
include MyEmailValidations

Does this solve your problem?


2010/4/1 Grary [email protected]


Yes, that was exactly what I needed.

I see I need to explore the specifics of mixing in (which maybe Matz’s
book underserves) – in this case it was the self.include(base)
expression that was key.

Finally, where attributes refer logically to the same kind of data,
but have different names, I have aliased them to allow the broadest
use of my version of your validation module.

Thanks so much,


Nice – glad you could use it :slight_smile:


2010/4/1 Grary [email protected]

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