Question

我希望使用ActiveRecord获取日期范围中的第一个和最后一个项目。我可以

BalanceLedger.where(created_at: Time.now-7.days..Time.now).order(:created_at).first

和

BalanceLedger.where(created_at: Time.now-7.days..Time.now).order(:created_at).last

获取每周范围内的第一个和最后一个，但是当我只查找2个条目时，这似乎会在每个查询中返回很多。

获得此范围内的第一个和最后一个最有效率是什么？

Answer 1

~~您不必运行两个查询。您可以运行一个查询，然后在其上调用first和last。~~

您可以通过以下方式改进代码，但无论如何都会运行这两个查询。感谢@muistooshort和@jordan在评论中指出这一点。

balance_ledgers = BalanceLedger.where(created_at: Time.now-7.days..Time.now).order(:created_at)
first_one = balance_ledgers.first
last_one  = balance_ledgers.last

修改

~~它实际上运行了一个查询，我在Rails控制台中检查了它。见下文：~~

>> users = User.where(created_at: Time.now-7.days..Time.now).order(:created_at) User Load (0.5ms) SELECT "users".* FROM "users" WHERE ("users"."created_at" BETWEEN $1 AND $2) ORDER BY "users"."created_at" ASC [["created_at", 2016-11-11 09:59:00 UTC], ["created_at", 2016-11-18 09:59:00 UTC]] => #<ActiveRecord::Relation [#<User id: 6, email: nil, first_name: nil, last_name: nil, username: "arslan_ali505", phone_number: nil, address: nil, created_at: "2016-11-14 16:02:27", updated_at: "2016-11-14 16:02:27", role_id: 7, temp_password: "P8ijrXZErI0=", temp_password_changed: false>, #<User id: 7, email: nil, first_name: nil, last_name: nil, username: "arslan_ali_arslan_ali170", phone_number: nil, address: nil, created_at: "2016-11-16 11:41:57", updated_at: "2016-11-16 18:58:37", role_id: 3, temp_password: "e27aad7b817354f3", temp_password_changed: true>, #<User id: 8, email: nil, first_name: "John", last_name: "Don", username: "jhondon213", phone_number: nil, address: nil, created_at: "2016-11-17 13:09:07", updated_at: "2016-11-17 13:09:43", role_id: 7, temp_password: nil, temp_password_changed: true>]> >> users.first => #<User id: 6, email: nil, first_name: nil, last_name: nil, username: "arslan_ali505", phone_number: nil, address: nil, created_at: "2016-11-14 16:02:27", updated_at: "2016-11-14 16:02:27", role_id: 7, temp_password: "P8ijrXZErI0=", temp_password_changed: false> >> users.last => #<User id: 8, email: nil, first_name: "John", last_name: "Don", username: "jhondon213", phone_number: nil, address: nil, created_at: "2016-11-17 13:09:07", updated_at: "2016-11-17 13:09:43", role_id: 7, temp_password: nil, temp_password_changed: true>

<击>

Answer 2

您也可以尝试sql查询＆amp;除了使用rails查询之外，它可以直接使用它，它也会改善执行时间。

ActiveRecord::Base.connection.execute("SQL query")

获取ActiveRecord日期范围查询中第一个和最后一个项目的最快方法？

2 个答案: