Question

我正在尝试使用ActiveRecord编写一个简单的EXISTS查询。由于某种原因，它似乎正在运行2个查询。

User.where("exists (select 'X' from roles where roles.role = 'teacher' and roles.user_id = users.id)")

从日志中

查询1

     (1.2ms)  SELECT COUNT(count_column) FROM (SELECT  1 AS count_column FROM "users" WHERE (users.id <> 3 and exists (select 'X' from roles where roles.role = 'teacher' and roles.user_id = users.id)) LIMIT $1 OFFSET $2) subquery_for_count  [["LIMIT", 2], ["OFFSET", 0]]

查询2

  User Load (1.0ms)  SELECT  "users".* FROM "users" WHERE (users.id <> 3 and exists (select 'X' from roles where roles.role = 'teacher' and roles.user_id = users.id)) LIMIT $1 OFFSET $2  [["LIMIT", 2], ["OFFSET", 0]]

有没有办法避免这种情况。我会直接在SQL中编写查询，如下所示：

SELECT u.*
FROM users u,
     roles r
WHERE r.user_id = u.id
 AND u.id <> #{@user.id}
 AND r.role = 'teacher'

在Rails ActiveRecord中对EXISTS进行不必要的第二次查询

0 个答案: