options_from_collection_for_select不允許通過變量選擇

Question

以下兩段代碼，options_from_collection_for_select適用於設置:selected當我使用設置值，但是當我使用@posts.user_id它失敗。

這是爲什麼這個工作？

select_tag "user-dropdown", options_from_collection_for_select(@users, 'id', 'fname', **11**), :class =>'form-control' 

但這不是嗎？

select_tag "user-dropdown", options_from_collection_for_select(@users, 'id', 'fname', **@posts.user_id**), :class =>'form-control' 

Answer 1

select_tag "user-dropdown", options_from_collection_for_select(@users, 'id', 'fname', **@posts.user_id**), :class =>'form-control' 

這是什麼@ posts.user_id你想在你的選項來顯示？

select_tag與options_for_select例如

使用options_for_select與select_tag

select_tag 'user_id', options_for_select(@users.collect{ |u| [u.name, u.id] }) 

這將產生類似的例子：

<select id="user_id" name="user_id"> 
    <option value="1">Brad</option> 
    <option value="2">Angie</option> 
    <option value="3">Jenny</option> 
</select>