ruby on rails - How to make Devise lockable with number of failed attempts

Question

Using Devise 2.1.2 and Rails 3.2.6

I'm doing this Q&A just in case others run into this problem because I found little and scattered documentation for it.

This error may occur if you try to set up Devise as lockable.

undefined local variable or method `locked_at' for [someClass]

It means your model doesn't have the appropriate attributes.

Prerequisites: Set up the following in config/initializers/devise.rb

# ==> Configuration for :lockable
# Defines which strategy will be used to lock an account.
# :failed_attempts = Locks an account after a number of failed attempts to sign in.
# :none            = No lock strategy. You should handle locking by yourself.
config.lock_strategy = :failed_attempts

# Defines which key will be used when locking and unlocking an account
config.unlock_keys = [ :email ]

# Defines which strategy will be used to unlock an account.
# :email = Sends an unlock link to the user email
# :time  = Re-enables login after a certain amount of time (see :unlock_in below)
# :both  = Enables both strategies
# :none  = No unlock strategy. You should handle unlocking by yourself.
config.unlock_strategy = :email

# Number of authentication tries before locking an account if lock_strategy
# is failed attempts.
config.maximum_attempts = 20

# Time interval to unlock the account if :time is enabled as unlock_strategy.
# config.unlock_in = 1.hour

Set up your model to include devise :lockable:

class Example < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :confirmable,
  # :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable, :lockable

Answer 1

Devise needs these three attributes on your model. Therefore, generate the following migration and run it.

class AddLockableToExamples < ActiveRecord::Migration
  def change
    add_column :examples, :failed_attempts, :integer, default: 0
    add_column :examples, :unlock_token, :string # Only if unlock strategy is :email or :both
    add_column :examples, :locked_at, :datetime
  end
end

Hope this saves someone else hours of google-fu.