在SQL中：

Question

我有一个视频模型和一个标签模型。标签HABTM视频和视频HABTM标签。

class Tag < ApplicationRecord
  has_and_belongs_to_many :videos
  scope :with_tag, -> (id) { where(id: id) }
end

class Video < ApplicationRecord
  has_and_belongs_to_many :tags
end

我想知道如何创建一个查询，其中来自用户的标签数量未知。所以我可以说：“给我看所有标有（123 AND 124 AND 125）的视频”。最终的目标是我不知道用户将传递多少标签，因此我需要知道如何创建范围链，最终能够将整个内容传递到ransack上以进行文本搜索。结果视频的某些字段。我该怎么做？

更新：我想知道如何用Rails和ActiveRecord做到这一点。我知道如何使用SQL完成此操作。但是，仅通过SQL来完成它不会使我将结果关系传递给ransack。

Answer 1

我创建了一些相关的表来编写此答案，并针对表中的数据测试查询。所以，我在这里获取帖子，它们的标签都为1和2。

在SQL中：

rails-test_development=# select id from posts;
 id
----
  1
  2
  3
(3 rows)

rails-test_development=# select id from tags;
 id
----
  2
  3
  4
  5
  6
(5 rows)

rails-test_development=# select post_id, tag_id from posts_tags;
 post_id | tag_id
---------+--------
       1 |      2
       2 |      3
       2 |      2
       2 |      1
       3 |      1
       3 |      2
       1 |      4
(7 rows)

rails-test_development=# WITH posts_tags_cte AS (
rails-test_development(#         SELECT post_id, array_agg(tag_id) as tags
rails-test_development(#         FROM posts_tags
rails-test_development(#         WHERE tag_id in (1, 2)
rails-test_development(#         GROUP BY post_id
rails-test_development(# )
rails-test_development-# SELECT posts.id FROM posts_tags_cte JOIN posts ON posts.id = posts_tags_cte.post_id
rails-test_development-# WHERE posts_tags_cte.tags @> array[1, 2]::int8[];
 id
----
  3
  2
(2 rows)

现在加入Rails：

rails-test$ rails c
Running via Spring preloader in process 7361
Loading development environment (Rails 5.2.1)
2.5.1 :001 > Post.by_tag([1,2]).first.attributes
  Post Load (1.7ms)  SELECT  "posts".* FROM     (WITH posts_tags_cte AS (
      SELECT post_id, array_agg(tag_id) as tags
      FROM posts_tags
      WHERE tag_id in (1,2)
      GROUP BY post_id
    )
    SELECT posts.* FROM posts_tags_cte JOIN posts ON posts.id = posts_tags_cte.post_id
    WHERE posts_tags_cte.tags @> array[1,2]::int8[]) as posts
 ORDER BY "posts"."id" ASC LIMIT $1  [["LIMIT", 1]]
 => {"id"=>2, "name"=>"Postppp", "title"=>"Post", "content"=>"I don't know", "created_at"=>Sun, 09 Sep 2018 09:48:33 UTC +00:00, "updated_at"=>Sun, 09 Sep 2018 09:48:33 UTC +00:00, "month_and_year"=>Sun, 09 Sep 2018}
2.5.1 :002 > Post.by_tag([1,2]).last.attributes
  Post Load (1.3ms)  SELECT  "posts".* FROM     (WITH posts_tags_cte AS (
      SELECT post_id, array_agg(tag_id) as tags
      FROM posts_tags
      WHERE tag_id in (1,2)
      GROUP BY post_id
    )
    SELECT posts.* FROM posts_tags_cte JOIN posts ON posts.id = posts_tags_cte.post_id
    WHERE posts_tags_cte.tags @> array[1,2]::int8[]) as posts
 ORDER BY "posts"."id" DESC LIMIT $1  [["LIMIT", 1]]
 => {"id"=>3, "name"=>"Post A", "title"=>"Post title", "content"=>"Lorem Ipsum is simply dummy text of the printing and typesetting industry.", "created_at"=>Sun, 09 Sep 2018 09:52:57 UTC +00:00, "updated_at"=>Sun, 09 Sep 2018 09:52:57 UTC +00:00, "month_and_year"=>Sun, 09 Sep 2018}
2.5.1 :003 >

我将范围定义为：

class Post < ApplicationRecord
  has_and_belongs_to_many :tags

  scope :by_tag, -> (tag_ids) {

    sql = sanitize_sql_array [<<-SQL, tag_ids, tag_ids]
    (WITH posts_tags_cte AS (
      SELECT post_id, array_agg(tag_id) as tags
      FROM posts_tags
      WHERE tag_id in (?)
      GROUP BY post_id
    )
    SELECT posts.* FROM posts_tags_cte JOIN posts ON posts.id = posts_tags_cte.post_id
    WHERE posts_tags_cte.tags @> array[?]::int8[]) as posts
    SQL

    from(sql)
  }
end

我从this answer那里得到了帮助。

如何动态链接Rails中的where子句？

1 个答案:

在SQL中：

现在加入Rails：