Proper ActiveRecord Uniqueness Validations¶ ↑

This is an attempt at getting non-racey uniqueness validations to work with ActiveRecord, this gem will monkey patch ActiveRecord’s create_or_update method to catch exceptions triggered by unique index violations on the database layer and add an error to the ActiveRecord instance in question when this happens.

So whats happening is that we’re just trying to insert or update the record in question and letting the database do it’s work and reject the operation if a unique index constraint is violated.

As a side effect, you can get rid of the regular uniqueness validations, losing potentially lots of database calls in the process.

Limitations¶ ↑

• Only works with Postgresql so far, since thats the only database I use for serious work nowadays. Patches welcome for other databases.

• Strict Validations are not supported.

• RSpecs model.should have(n).errors_on(:attribute) doesn’t work; try using model.errors.messages.keys.should include(:attribute) after a save operation.

Usage¶ ↑

First, set up unique indexes for what you need kept unique (but you already had those, right?).

Add the gem to your Gemfile:

gem 'proper_active_record_uniqueness_validations', 
     :require => 'proper_uniqueness_validation'

Then, adjust the models in question as follows:

class MyModel < ActiveRecord::Base
  # Override create_or_update
  include ProperUniquenessValidation

  # Specify for each uniqueness index, which attribute should get an error
  # attached to it. This is the easiest way of dealing with postgres' indexing
  # possibilities such as functions etc.
  uniqueness_error_attribute_for 'index_my_models_attribute', 
                                 :attribute_to_add_error_to

  # ...
  # your other code here
end

You may need to adjust your tests/specs, since the errors will only get attached when the actual save takes place. Calling valid? will not work, unless you keep your traditional uniqueness validations explicitly around.