Sql 如何通过Rails模型在Postgres上按日期分组
我将Postgres与Ruby on Rails结合使用，并希望在away中查询我的Sql 如何通过Rails模型在Postgres上按日期分组,sql,ruby-on-rails,postgresql,activerecord,arel,Sql,Ruby On Rails,Postgresql,Activerecord,Arel,我将Postgres与Ruby on Rails结合使用，并希望在away中查询我的posts表，该表返回按创建日期分组的所有posts，每组按时间顺序排列 我的目标的一个完美例子是，任何一个博客的索引都会按日期列出所有帖子 我希望得到的伪代码对象结构类似于： posts_grouped_by_date = { "1/2/2014" => [post1, post2, post3], "1/15/2014" => [post5, post6,post7], etc.. }
postsposts_grouped_by_date = {
"1/2/2014" => [post1, post2, post3],
"1/15/2014" => [post5, post6,post7],
etc..
}
posts id | title | created_at
----+-------------------------------------------------------------------+----------------------------
13 | Eaque hic tenetur at quam quibusdam eveniet veritatis. | 2014-08-18 02:40:31.329665
9 | The only thing i want to say. | 2014-08-18 02:40:31.329665
16 | Est sunt cumque rerum nam nobis consequuntur aut. | 2014-08-19 02:58:26.817936
18 | Fuga assumenda facilis aut mollitia eum soluta. | 2014-08-19 02:58:26.837839
8 | The only thing i want to say. | 2014-08-18 02:40:31.329665
12 | Laudantium dolores odit sed veritatis in et vel deserunt. | 2014-08-18 02:40:31.329665
10 | The only thing i want to say. | 2014-08-18 02:40:31.329665
20 | Rem laboriosam ipsam sunt maxime quia adipisci et voluptatem. | 2014-08-19 02:58:26.837839
19 | Laudantium sit explicabo et quia eligendi ipsam. | 2014-08-19 02:58:26.837839
21 | Repellat qui eos dolorem. | 2014-08-19 02:58:26.837839
6 | The only thing i want to say. | 2014-08-18 02:40:31.329665
17 | Error voluptatem architecto distinctio impedit iste dolores enim. | 2014-08-19 02:58:26.829968
15 | Vero modi voluptate deleniti labore quis est. | 2014-08-19 02:58:26.808126
14 | Et neque porro qui animi facilis numquam. | 2014-08-19 02:58:26.800474
Post.order(:created_at).group_by {|p| p.created_at.to_date}
我将如何使用ActiveRecord或Arel语法来实现这一点？代码背后的解释也会非常有用。我用它来学习/练习，而不仅仅是复制/粘贴。我想你想要这样的东西：
id | title | created_at
----+-------------------------------------------------------------------+----------------------------
13 | Eaque hic tenetur at quam quibusdam eveniet veritatis. | 2014-08-18 02:40:31.329665
9 | The only thing i want to say. | 2014-08-18 02:40:31.329665
16 | Est sunt cumque rerum nam nobis consequuntur aut. | 2014-08-19 02:58:26.817936
18 | Fuga assumenda facilis aut mollitia eum soluta. | 2014-08-19 02:58:26.837839
8 | The only thing i want to say. | 2014-08-18 02:40:31.329665
12 | Laudantium dolores odit sed veritatis in et vel deserunt. | 2014-08-18 02:40:31.329665
10 | The only thing i want to say. | 2014-08-18 02:40:31.329665
20 | Rem laboriosam ipsam sunt maxime quia adipisci et voluptatem. | 2014-08-19 02:58:26.837839
19 | Laudantium sit explicabo et quia eligendi ipsam. | 2014-08-19 02:58:26.837839
21 | Repellat qui eos dolorem. | 2014-08-19 02:58:26.837839
6 | The only thing i want to say. | 2014-08-18 02:40:31.329665
17 | Error voluptatem architecto distinctio impedit iste dolores enim. | 2014-08-19 02:58:26.829968
15 | Vero modi voluptate deleniti labore quis est. | 2014-08-19 02:58:26.808126
14 | Et neque porro qui animi facilis numquam. | 2014-08-19 02:58:26.800474
Post.order(:created_at).group_by {|p| p.created_at.to_date}
2-然后，一旦你订购了所有的帖子，你就可以使用块中的代码对它们进行分组。由于您不希望时间戳包含在分组中（每秒钟都有不同的记录，这有什么意义呢？），因此您可以将时间戳转换为日期。这是可行的，但需要在运行
group\u by