Factory Girl中的association不是引用而是创建么？

[run27017]

我正在使用Mongoid，所以fixtures用不了了，用factory_girl进行替代。定义两个Model：

    class User
      include Mongoid::Document

      field name, type: String
      validates :name, uniquess: true
    end

    class Post
      include Mongoid::Document

      belongs_to :user
    end

然后定义几个工厂：

FactoryGirl.define do
  factory :user do #这会创建user
    name 'user'
  end
end

FactoryGirl.define do
  factory :post1, class: 'Post' do
    user #这会创建user
  end
end

FactoryGirl.define do
  factory :post2, class: 'Post' do
    user #这会创建user
  end
end

我是测试新手，不知道factory girl的使用习惯。我沿用fixtures的思维，在测试之前提前准备好数据库，使用下面的语句：

Mongoid::default_client.database.drop
FactoryGirl.lint

然后报错：

rake aborted!
FactoryGirl::InvalidFactoryError: The following factories are invalid:

* user - 
message:
Validation of User failed.
summary:
The following errors were found: Name is already taken
resolution:
Try persisting the document with valid data or remove the validations. (Mongoid::Errors::Validations)/home/hello/workspace/scaffold/vendor/bundle/ruby/2.1.0/gems/factory_girl-4.5.0/lib/factory_girl/linter.rb:14:in `lint!'
。。。