Rubyonrails FactoryGirl + Faker 为数据库种子数据中的每个对象生成相同的数据

我正在使用FactoryGirl和Faker在我的seeds.rb文件中生成用户对象，但由于某些原因，正在创建完全相同的用户，rake db:seed由于邮箱唯一性验证而失败.

用户工厂:

#users.rb
require 'faker'

FactoryGirl.define do
  factory :user do
    first_name            Faker::Name.first_name
    last_name             Faker::Name.last_name
    phone                 Faker::PhoneNumber.cell_phone
    email                 Faker::Internet.email
    password              "password"
    password_confirmation "password"
  end
end

seeds.rb文件中的代码:

#seeds.rb
rand(5..11).times { FactoryGirl.create(:user) }

错误:

ActiveRecord::RecordInvalid: Validation failed: Email has already been taken

如果我打开控制台并使用FactoryGirl.create(:user)，我会得到同样的结果...同一个对象被一次又一次地创建，即使我只运行Faker::Internet.email几次，也会收到几封邮箱.

工厂女孩:

[1] pry(main)> FactoryGirl.create(:user)
...
=> #<User id: 3, first_name: "Osvaldo", last_name: "Wunsch", email: "willy@damore.net", phone: "(912)530-4949 x64848", created_at: "2014-07-31 20:57:27", updated_at: "2014-07-31 20:57:27", encrypted_password: "$2a$10$mxWC7yLYR0m/Sw8MO6Lyru.xuTHCdCEuM9Orx3LXGApF...", reset_password_token: nil, reset_password_sent_at: nil, remember_created_at: nil, sign_in_count: 0, current_sign_in_at: nil, last_sign_in_at: nil, current_sign_in_ip: nil, last_sign_in_ip: nil>
[2] pry(main)> FactoryGirl.create(:user)
...
ActiveRecord::RecordInvalid: Validation failed: Email has already been taken

骗子本身:

[3] pry(main)> Faker::Internet.email
=> "hobart_purdy@goodwinmills.org"
[4] pry(main)> Faker::Internet.email
=> "pierce_brekke@gislasonrolfson.net"

我错过了什么？为什么Faker每次通过FactoryGirl使用时都会产生相同的数据？