我試了一下 assign_attributes, 

````ruby
    issue =  FactoryGirl.create(:issue)
    puts issue.inspect
    issue.assign_attributes({:id => 50000, :user_id => user.id, :order_id => 50000000, :content => "123123"})
    puts issue.inspect
    Issue.new(FactoryGirl.create(:issue).assign_attributes({:id => nil, :user_id => user.id, :order_id => @order.id})).save.should be_false
````
http://d.pr/i/9RfU
這樣會是綠燈沒錯, 不過ID還是沒辦法修改, 不過我發現assign_attributes 回傳的值是nil,  這樣根本不太對XDD

所以我只好改為相同意思的簡單寫法

````ruby
Issue.new(:user => user, :order => @order ).save.should be_false
````