Uniqueness validation does not guarantee uniqueness. Only the database constraints do this. But there is a flaw - when database constraints fail, an exception is thrown, and even when we catch it, the validation error is not set.

This gem solves the issue.

It catches the database constraints exception, revalidates and returns false from save. To use it, you should set both validation and database constraint. Then even if uniqueness validation mistakenly let you in, it will break the database constraint, then revalidate and the validation will tell you the truth.

Add this line to your application's Gemfile:

gem 'cerbero'

Say you need the uniqueness of email inside the company_id. In your model you should say:

validates :email, uniqueness: {scope: :company_id}

and in your migration:

add_index :users, [:email, :company_id], unique: true

Important: you should add both validation and db constraint. If you don't supply validation, you'll have save returning false, yet no validation errors will be displayed, which is a strange and obscure behavior.

Then if the gem is required, it makes the stuff work so that when the uniqueness validtion lets you in, but the database constraint then fails, save returns false, then uniqueness validation is re-run and the execution flow goes like the uniqueness validation worked perfectly.

Use it! Provide me the issues if found. If you are really willing to provide some code:

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

• Andry Conchin

• Apply a cleaner pattern to test via multiple databases.
• Add travis-ci - it's broken for some reason.
• Extract the save monkey-patch to module and apply the alias_method_chain pattern to avoid possible collisions.
• Add an option to apply the gem per-model basis.