Question

设置：Rails 3.2.18，Postgres

我有两个对象，例如，使用以下设置调用Author和Article：

class Author
  has_many :articles

  ...
end

class Article
  belongs_to :author

  class << self

    def published_over_one_year_ago
      where(arel_table[:published_at].lt(1.year.ago))
    end

  end
end

我试图找到所有Author条记录，其中所有关联的Article记录都是在一年前发布的。这段代码：

Author.joins(:article).merge(Article.published_over_one_year_ago)

...返回Author个对象，其中至少一个关联Article在一年前发布，但我只需要 {{ 1}}记录所有关联的Author记录超过一年的记录。这是可能的arel / ActiveRecord，还是我必须使用原始SQL？

潜在的＆＃34;工作＆＃34; SQL解决方案：

Article

更新我看到已经有一个使用arel的建议答案，这是非常出色的。如果可能，任何人都有建议使用直接ActiveRecord吗？

Answer 1

使用Arel和公用表表达式：

articles = Article.arel_table
authors = Author.arel_table
cte_table = Arel::Table.new(:cte_table)
composed_cte =
     Arel::Nodes::As.new(cte_table,
                         articles.project(articles[:author_id],
                                          articles[:published_at].maximum.as("max_published_at"))
                                 .group(articles[:author_id])
                        )

然后：

authors
  .join(cte_table).on(cte_table[:author_id].eq(authors[:id]))
  .with(composed_cte)
  .where(cte_table[:max_published_at].lt(1.year.ago))
  .project(authors[:id])
  .to_sql

返回（为清晰起见而格式化）：

WITH "cte_table" AS (
    SELECT articles.author_id,
           MAX(articles.published_at) AS max_published_at
    FROM articles
    GROUP BY articles.author_id
)
SELECT authors.id
FROM authors
INNER JOIN cte_table
ON cte_table.author_id = authors.id
WHERE cte_tble.max_published_at < '2014-01-25 23:04:16.532796'

使用它：

这

[2] test»  Article.pluck(:author_id, :published_at)                                                                                                                                    
D, [2015-01-26T00:10:06.763197 #21897] DEBUG -- :    (0.6ms)  SELECT "articles"."author_id", "articles"."published_at" FROM "articles"
=> [
  [0] [
    [0] 1,
    [1] Sun, 25 Jan 2015 23:31:58 UTC +00:00
  ],
  [1] [
    [0] 1,
    [1] Fri, 01 Jan 1999 00:00:00 UTC +00:00
  ],
  [2] [
    [0] 2,
    [1] Fri, 01 Jan 1999 00:00:00 UTC +00:00
  ]

查询返回：

[2015-01-26T00:10:25.279587 #21897] DEBUG -- :    (0.9ms)  WITH "cte_table" AS (SELECT "articles"."author_id", MAX("articles"."published_at") AS max_published_at FROM "articles" GROUP BY "articles"."author_id") SELECT "authors"."id" FROM "authors" INNER JOIN "cte_table" ON "cte_table"."author_id" = "authors"."id" WHERE "cte_table"."max_published_at" < '2014-01-25 23:10:25.277902'
=> [
  [0] {
    "id" => "2"
  }
]

修改

不使用Arel：

Author.joins(:articles) .where("authors.id != ANY (?)", Article.select('author_id') .where("published_at > ?", 1.year.ago) )

如果您将.published_last_year添加到文章：

class Article < ActiveRecord::Base belongs_to :author def self.published_last_year where("published_at > ?", 1.year.ago) end end

然后

Author.joins(:articles) .where("authors.id != ANY (?)", Article.published_last_year.select('author_id'))

Rails4版本

Author.joins(:articles) .where.not(id: Article.published_last_year.select('author_id'))

Rails：仅返回所有关联满足条件的对象

1 个答案: