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Ruby gem to rescue from MySQL, PostgreSQL and Sqlite duplicate errors
Ruby Groff
Latest commit 009098f Jun 9, 2016 @byroot byroot Release 0.1.1

ActiveRecord - RescueFromDuplicate

Build Status

This gem will rescue SQL errors when trying to insert records that fail uniqueness validation.

It complements :validates_uniqueness_of and will add appropriate errors.

Additionally, a macro allows you to assume that the record will be unique and rescue gracefully otherwise.

Tested with:

  • ActiveRecord: 3.2, 4.0, 4.1, 4.2, edge
  • Ruby 1.9.3, 2.0.0, 2.1.2
  • MySQL, PostgreSQL, Sqlite3


  • after_validation, before_save, before_create will have been run. Make sure they don't have undesired side-effects.
  • Unlike failed validation, ActiveRecord::RecordNotSaved will be raised when using create!, save! or other ! methods.


With validation

Add the rescue_from_duplicate: true to any regular uniqueness validation.

This will use the Rails standard validation, performing a SELECT to ensure the record is valid. In the case of a race condition, an error will be added to the model, and no exception will be thrown.

class ModelWithUniquenessValidator < ActiveRecord::Base
  validates_uniqueness_of :name, scope: :shop_id, rescue_from_duplicate: true

If two of this statement go in at the same time, and the original validation on uniqueness of name passes, the DBMS will raise an duplicate record error.

a = ModelWithUniquenessValidator.create(name: "name")

# in a different thread, causing race condition
b = ModelWithUniquenessValidator.create(name: "name")

a.persisted? #=> true
b.persisted? #=> false
b.errors[:name] #=> ["has already been taken"]

Without validation

You can use this if you don't need to check that the record is unique before attempting to insert it. It will not add any validation to the model, but it will add an error if the persistance fails.

class ModelWithUniqueToken < ActiveRecord::Base
  rescue_from_duplicate :token, scope: :shop_id


Add this line to your application's Gemfile:

gem 'activerecord-rescue_from_duplicate'

And then execute:

$ bundle

Or install it yourself as:

$ gem install activerecord-rescue_from_duplicate


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