constancy.rubyforge.org

Compatible with Rails v1.2.2 through v2.0.4 (Active Record v1.15.2 through v2.0.4)

This Rails plugin adds a validates_constancy_of validation to Active Record. It allows you to prevent particular database fields from being changed after a record is created. A validation error occurs on updates if an attribute of a model object is different from its value in the database.

The code is packaged as a Rails plugin. It is compatible with the latest released version of the Rails framework (and possibly also other versions – see the ‘test’ branch of this repository). You can install the plugin with the command:

ruby script/plugin install git://github.com/njonsson/validates-constancy-rails-plugin.git

Here’s how to use this validation in your code.

class Person < ActiveRecord::Base

  # Prevent changes to Person#social_security_number.
  validates_constancy_of :social_security_number

end

The validation takes two options, :if and :message. These may be familiar because several of Active Record’s validations also use them. The :if option takes a Proc, or a symbol, or string with a model object argument and a return value of true or false.

class Comment < ActiveRecord::Base

  # Prevent changes to Comment#text if it is "locked."
  validates_constancy_of :text, :if => Proc.new { |comment| comment.locked? }

end

The default error message is “can’t be changed”. Use your own error message by specifying the :message option.

class LicensePlate < ActiveRecord::Base

  # Prevent changes to LicensePlate#number.
  validates_constancy_of :number,
                         :message => 'is off-limits! What are you thinking?'

end

More than one model attribute can be specified. Any specified options will be applied to all the specified attributes.

With associations, validate the constancy of a foreign key, not the instance variable itself: validates_constancy_of :invoice_id instead of validates_constancy_of :invoice.

Also note the warning under Inheritable callback queues in api.rubyonrails.org/classes/ActiveRecord/Callbacks.html. “In order for inheritance to work for the callback queues, you must specify the callbacks before specifying the associations. Otherwise, you might trigger the loading of a child before the parent has registered the callbacks and they won’t be inherited.” Validates Constancy uses these callback queues, so you’ll want to specify associations after validates_constancy_of statements in your model classes.

There’s a suite of tests that exercises all the functionality of Validates Constancy. You can check out a version of the test suite from the repository according to the version of Rails (Active Record) it works with.

git checkout test
git submodule update --init

Then read rails_*/doc/README_FOR_APP for instructions on how to run the tests.

Copyright © 2007-2009 Nils Jonsson (nils@alumni.rice.edu)

Released under the MIT license.