Ruby-on-rails Rails ActiveRecord : 加入 LEFT JOIN 而不是 INNER JOIN
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Rails ActiveRecord :joins with LEFT JOIN instead of INNER JOIN
提问by Jakub Arnold
I have this code
我有这个代码
User.find(:all, :limit => 10, :joins => :user_points,
:select => "users.*, count(user_points.id)", :group =>
"user_points.user_id")
which generates following sql
生成以下sql
SELECT users.*, count(user_points.id)
FROM `users`
INNER JOIN `user_points`
ON user_points.user_id = users.id
GROUP BY user_points.user_id
LIMIT 10
is it possible to make LEFT JOIN instead of INNER JOIN other way than User.find_by_sqland manualy typing the query?
除了User.find_by_sql手动输入查询之外，是否可以使用 LEFT JOIN 而不是 INNER JOIN ？
回答by Kylo
You can try this
你可以试试这个
User.find(:all, limit: 10,
joins: "LEFT JOIN `user_points` ON user_points.user_id = users.id" ,
select: "users.*, count(user_points.id)",
group: "user_points.user_id")
回答by 8bithero
Just for future reference, adding :allgives a deprecated message. In later versions of rails you can simply chain the methods like this:
仅供将来参考，添加:all会给出一条已弃用的消息。在更高版本的 rails 中，您可以简单地将方法链接如下：
User.joins("LEFT JOIN `user_points` ON user_points.user_id = users.id").select("users.*, count(user_points.id)").group("user_points.user_id")
OR use a scopelike this:
或者使用这样的范围：
scope :my_scope_name_here, -> {
joins("LEFT JOIN `user_points` ON user_points.user_id = users.id")
.select("users.*, count(user_points.id)")
.group("user_points.user_id")
}
You can also chain .wherebetween the .joinand the .select.
Hope this helps someone in the future.
您还可以.where在.join和之间进行链接.select。希望这对未来的人有所帮助。
回答by Santhosh
Rails 5 has a left_outer_joinsmethod. So you can do
Rails 5 有一个left_outer_joins方法。所以你可以做
User.left_outer_joins(:user_points)
or use the alias
或使用别名
User.left_joins(:user_points)
