Question

我有一个Article，每个Article 完全一个User而为零或一个 ArticleVote

我的代码是：

@articles = Article
    .eager_load(:user)
    .eager_load(:article_vote)
    .where(article_votes: { user_id: session[:user_id]})
    .order(created_at: :desc)

产生以下SQL：

SELECT
    `articles`.`article_id` AS t0_r0,
    `articles`.`user_id` AS t0_r1,
    `users`.`user_id` AS t1_r0,
    `article_votes`.`article_vote_id` AS t2_r0,
    `article_votes`.`article_id` AS t2_r1,
    `article_votes`.`user_id` AS t2_r2
FROM `articles`
LEFT OUTER JOIN `users` ON `users`.`user_id` = `articles`.`user_id`
LEFT OUTER JOIN `article_votes` ON `article_votes`.`article_id` = `articles`.`article_id`
WHERE `article_votes`.`user_id` = 1
ORDER BY `articles`.`created_at` DESC

此查询的问题是如果不存在投票（有时它赢了），则不会返回任何记录。我真正需要的是这个（注意哪里已经消失，条件被移到左边的连接处）：

SELECT
    `articles`.`article_id` AS t0_r0,
    `articles`.`user_id` AS t0_r1,
    `users`.`user_id` AS t1_r0,
    `article_votes`.`article_vote_id` AS t2_r0,
    `article_votes`.`article_id` AS t2_r1,
    `article_votes`.`user_id` AS t2_r2
FROM `articles`
LEFT OUTER JOIN `users` ON `users`.`user_id` = `articles`.`user_id`
LEFT OUTER JOIN `article_votes` ON `article_votes`.`article_id` = `articles`.`article_id` and `article_votes`.`user_id` = 1
ORDER BY `articles`.`created_at` DESC

我在文档中看到我可以做类似的事情：

has_one :article_vote, -> { where(user_id: 1) }

哪个会将它放在左边的连接中，而不是在哪里，但是这不允许我在查询时指定user_id，这使得它不可行。

可以这样做吗？

Rails 4 - 渴望加载多个ON条件

0 个答案: