对 MongoDB 查询进行排序会导致返回的行数减少

发布于 2024-11-09 14:00:19 字数 1433 浏览 0 评论 0原文

我在 Mongoid（2.0.0.beta.17 和 2.0.2）/MongoDB 中排序时遇到问题。也许我对 MongoDB 的经验还不够，你们中的一些人可以帮助我理解我做错了什么？

用户级别的症状是：

查询未按日期或 ID 正确排序
用户帖子在看起来应该出现时却没有出现（这是类似 Twitter 的园丁社交网站，最近的帖子有时不会显示）

irb(main):024:0> Update.all.size

=> 551

Update.ordered.size     # (see below for definition)

=> 490

irb(main):010:0> Update.all.select{|u| u.created_at.nil?}

=> []

当我进入 mongo shell 并执行以下操作时：

var cursor = db.updates.find({}, {'_id': 1}).limit(600); 
while (cursor.hasNext()) printjson(cursor.next());

我返回 454 行。

var cursor = db.updates.find({}, {'_id': 1}).sort({created_at : 1}).limit(600); 
while (cursor.hasNext()) printjson(cursor.next());

还返回 454 行。

db.updates.find({}).sort({created_at: -1}).limit(1);

返回 2 月 23 日的更新。但我在 MongoDB 中有昨天的更新。有什么想法吗？

我的模型是：

class Update 
  include Mongoid::Document 
  include Mongoid::Timestamps 
  include Paperclip 
  field :body 
  ... 
  index [[ :created_at, Mongo::DESCENDING ]] 
  ... 
  named_scope :ordered, :order_by => ([[:created_at, :desc]]) 
  ... 
end

原文

I'm having an issue with ordering in Mongoid (2.0.0.beta.17 and 2.0.2)/MongoDB. Perhaps I'm just not experienced enough with MongoDB, and some of you can help me understand what I'm doing wrong?

The user-level symptoms are:

Queries not sorting correctly by date or ID
User posts are not appearing when they seem like they should be (this is a Twitter-like social networking site for gardeners, and the most recent posts are sometimes not showing up)

irb(main):024:0> Update.all.size

=> 551

Update.ordered.size     # (see below for definition)

=> 490

irb(main):010:0> Update.all.select{|u| u.created_at.nil?}

=> []

When I go into the mongo shell, and do:

var cursor = db.updates.find({}, {'_id': 1}).limit(600); 
while (cursor.hasNext()) printjson(cursor.next());

I get 454 lines returned.

var cursor = db.updates.find({}, {'_id': 1}).sort({created_at : 1}).limit(600); 
while (cursor.hasNext()) printjson(cursor.next());

Also returns 454 lines.

db.updates.find({}).sort({created_at: -1}).limit(1);

returns an update from February 23rd. But I have updates from yesterday in MongoDB.
Any ideas?

My model is:

class Update 
  include Mongoid::Document 
  include Mongoid::Timestamps 
  include Paperclip 
  field :body 
  ... 
  index [[ :created_at, Mongo::DESCENDING ]] 
  ... 
  named_scope :ordered, :order_by => ([[:created_at, :desc]]) 
  ... 
end

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这个俗人 2024-11-16 14:00:19

你能打印出 created_at 字段吗？

db.updates.find({}, {created_at:1}).sort({created_at: -1}).forEach(printjson)

您可能对保存日期字段的方式有疑问。输出是字符串吗？ ISODate()？

Can you print out the created_at field?

db.updates.find({}, {created_at:1}).sort({created_at: -1}).forEach(printjson)

You may have an issue with how you're saving your date fields. Is the output there a string? an ISODate()?

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那片花海 2024-11-16 14:00:19

我不明白为什么，但执行以下操作似乎可以解决问题：

named_scope :ordered, :order_by => ([[:created_at, :desc], [:_id, :desc]])

二次排序似乎有帮助。

irb(main):022:0> update = Update.order_by([[:created_at, :desc], [:_id, :desc]])

irb(main):025:0> update.count
=> 556
irb(main):026:0> update.first.created_at
=> Sat May 28 02:53:33 -0700 2011
irb(main):027:0> update.second.created_at
=> Fri May 27 17:55:38 -0700 2011
irb(main):028:0> update.first.created_at.class
=> Time
irb(main):029:0> update.second.created_at.class
=> Time

其中第一个被排除在原始查询之外。

I didn't figure out WHY, but doing the following seems to fix the problem:

named_scope :ordered, :order_by => ([[:created_at, :desc], [:_id, :desc]])

It seems the secondary ordering helps.

irb(main):022:0> update = Update.order_by([[:created_at, :desc], [:_id, :desc]])

irb(main):025:0> update.count
=> 556
irb(main):026:0> update.first.created_at
=> Sat May 28 02:53:33 -0700 2011
irb(main):027:0> update.second.created_at
=> Fri May 27 17:55:38 -0700 2011
irb(main):028:0> update.first.created_at.class
=> Time
irb(main):029:0> update.second.created_at.class
=> Time

The first of these was being left out of the original query.

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