Rails error on migration, rake aborted

Question

I have this migration to the table users made with Devise, all worked fine until i tried to make a back office with active_admin gem and added a role, etc:

 class DeviseCreateUsers < ActiveRecord::Migration
  def change
    create_table(:users) do |t|
    ## Database authenticatable
    t.string :username,           null: false, default: ""
    t.string :email,              null: false, default: ""
    t.string :encrypted_password, null: false, default: ""


    ## Recoverable
    t.string   :reset_password_token
    t.datetime :reset_password_sent_at

    ## Rememberable
    t.datetime :remember_created_at

    ## Trackable
    t.integer  :sign_in_count, default: 0, null: false
    t.datetime :current_sign_in_at
    t.datetime :last_sign_in_at
    t.string   :current_sign_in_ip
    t.string   :last_sign_in_ip

    ## Confirmable
    t.string   :confirmation_token
    t.datetime :confirmed_at
    t.datetime :confirmation_sent_at
    t.string   :unconfirmed_email # Only if using reconfirmable


    t.timestamps


    end

    add_index :users, :email,                unique: true
    add_index :users, :username,             unique: true
    add_index :users, :reset_password_token, unique: true
    add_index :users, :confirmation_token,   unique: true
    # add_index :users, :unlock_token,         unique: true
  end
end

And this migration that add a column to the table:

class AddRoleToUsers < ActiveRecord::Migration

  def change
      add_column :users, :role, :string

      User.create! do |u|
          u.username  = 'admin'
          u.email     = 'admin@example.com'
          u.password    = 'admin123'
          u.role = 'administrator'
      end
  end
end

I do rake db:migrate and got this error:

rake aborted!
StandardError: An error has occurred, this and all later migrations      canceled:

Record invalido/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-  4.2.1/lib/active_record/validations.rb:79:in `raise_record_invalid'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/validations.rb:43:in `save!'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/attribute_methods/dirty.rb:29:in `save!'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/transactions.rb:291:in `block in save!'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord- 4.2.1/lib/active_record/transactions.rb:347:in `block in  with_transaction_returning_status'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract/database_statements.rb:211:in `transaction'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/transactions.rb:220:in `transaction'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/transactions.rb:344:in `with_transaction_returning_status'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/transactions.rb:291:in `save!'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/persistence.rb:51:in `create!'           /home/dev8/RedTwitter/db/migrate/20150605140226_add_role_to_users.rb:6:in `change'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/migration.rb:606:in `exec_migration'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/migration.rb:590:in `block (2 levels) in migrate'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/migration.rb:589:in `block in migrate'
/home/dev8/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:292:in `with_connection'
........

I tried rake db:rollback and got a similar error. What could it be?

EDIT: User.rb

class User < ActiveRecord::Base

devise :database_authenticatable, :registerable,
     :recoverable, :rememberable, :trackable, :validatable,      :registerable, :confirmable, :authentication_keys => [:login]
 attr_accessor :login
 has_many :tweets , dependent: :destroy
 validates :username,
   :presence => true,
   :uniqueness => {
   :case_sensitive => false
    }, length: { in: 6..20 }


  def role?(role)
     roles.include? role.to_s
  end

  def login=(login)
     @login = login
  end

  def login
     @login || self.username || self.email
  end

  def self.find_for_database_authentication(warden_conditions)
      conditions = warden_conditions.dup
      if login = conditions.delete(:login)
      where(conditions.to_hash).where(["lower(username) = :value OR  lower(email) = :value", { :value => login.downcase }]).first
      else
        where(conditions.to_hash).first
      end
  end

end

Answer 1

Use find or create method. This will allow you to not raise invalid record error if you already have user, so all later migrations will run well.

Answer 2

class AddRoleToUsers < ActiveRecord::Migration

  def change
      add_column :users, :role, :string
      User.reset_column_information
      u = User.new
      u.username  = 'admin'
      u.email     = 'admin@example.com'
      u.password    = 'admin123'
      u.role = 'administrator'
      u.save(:validate => false)
  end
end

Answer 3

I believe you need to call User.reset_column_information in your migration, after adding the new column, otherwise Rails doesn't know about it.