Question

你好我發現了很多關於如何使用LEFT OUTER JOIN的例子，但我似乎無法找到訪問我加入的方法。這裏是我的意思是：

List.featured. 
    joins(
    "LEFT OUTER JOIN follows ON (
     follows.followable_id = lists.id AND 
     follows.followable_type = 'List' AND 
     follows.user_id = #{current_user.id})" 
).map { |list| 
    list.follows # <-- returns all follows, not only the ones from current_user 
    ... 

在這個例子中，我得到了如下（似乎）與加盟，但我又如何能訪問它們？ follows關係只會給我所有關於它似乎的列表。

或者，也許我的頭腦是霧:)謝謝！

Answer 1

躍躍欲試負荷如下，您可以撥打includes()：

List.featured.includes(:follows).where(:follows => { :user_id => current_user.id }) 

它會產生這樣的疑問：

SELECT 
    "lists"."id"   AS t0_r0, 
    "lists"."is_featured" AS t0_r1, 
    "lists"."created_at" AS t0_r2, 
    "lists"."updated_at" AS t0_r3, 
    "follows"."id"    AS t1_r0, 
    "follows"."followable_id" AS t1_r1, 
    "follows"."followable_type" AS t1_r2, 
    "follows"."user_id"   AS t1_r3, 
    "follows"."created_at"  AS t1_r4, 
    "follows"."updated_at"  AS t1_r5 
FROM 
    "lists" 
LEFT OUTER JOIN 
    "follows" 
ON 
    "follows"."followable_id" = "lists"."id" AND 
    "follows"."followable_type" = 'List' 
WHERE 
    "lists"."is_featured" = 't' AND 
    "follows"."user_id" = 1