[英]Rails: Return only objects where all associations meet a condition
設置:Rails 3.2.18,Postgres
我有兩個對象,例如,將它們命名為Author
和Article
,具有以下設置:
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
我試圖找到所有Author
所有相關的記錄Article
記錄發表了一年前。 這段代碼:
Author.joins(:article).merge(Article.published_over_one_year_ago)
...返回Author
對象,其中至少一個相關Article
在一年前發布,但我只需要Author
記錄,其中所有相關Article
記錄都超過一年。 這是可能的arel / ActiveRecord,還是我必須使用原始SQL?
潛在的“工作”SQL解決方案:
query = ERB.new(<<-SQL_END).result(binding)
'author'.id in (
select art.author_id
from articles art
group by art.author_id
having sum(case (art.published_at::date >= current_date) when true then 1 else 0 end) = 0 AND
sum(case(art.published_at::date < current_date) when true then 1 else 0 end) > 0
)
SQL_END
# The following now appears to do what I want it to do.
Author.includes(:articles).where(query)
更新我看到已經有一個建議的答案使用arel,這是傑出的。 如果可能的話,有人建議使用直接的ActiveRecord嗎?
使用Arel和公用表表達式:
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(為清晰起見而格式化):
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 :
從
[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
]
查詢返回:
[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"
}
]
編輯
不使用Arel:
Author.joins(:articles)
.where("authors.id != ANY (?)",
Article.select('author_id')
.where("published_at > ?", 1.year.ago)
)
如果您將.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'))
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.