如何在猫鼬中找到随机记录 [英] How to find random record in Mongoose

问题描述

如何在 MongoDB 中查找随机记录?

How can I find random records in MongoDB?

我在 StackOverflow 上找到了多篇文章，但我无法理解它们.例如:

I found multiple articles here on StackOverflow, but I couldn't understand them. Like for example:

db.yourCollection.find().limit(-1).skip(yourRandomNumber).next()

我将如何在我的代码中执行它?(集合是User)

How would I execute it in my code? (collection is User)

User.findOne(RANDOM PLAYER).then(result) {
    console.log(result);
}

推荐答案

获取随机记录背后的想法是查询所有匹配的记录，但只获取一个.这就是 findOne() 在没有给出任何标准的情况下所做的.

The idea behind getting a random record is to query all the matching records but just get one. This is what findOne() does without any criteria given.

然后您需要在所有可能的匹配项中随机选择一个条目.这是通过以下方式完成的:

Then you will want to pick a random entry in all the possible matches. This is done by:

1. 找出可能有多少可能的条目 - 为此，我们在集合上使用 count().请注意，如评论中所述，count 在第 4 版中已弃用，应使用 estimatedDocumentCount 或 countDocuments 代替.不同之处在于精度/内存使用等.这是一篇SO 的帖子，对其进行了一些讨论.

1. Find out how many possible entries there could be - we use count() on the collection for this. Note that, as mentioned in comments, count is deprecated in version 4 and one should use estimatedDocumentCount or countDocuments instead. The different lies in precision/memory usage amongst other things. Here's a SO post discussing it a bit.

在我们的计数范围内找出一个随机数.

Come up with a random number within our count.

使用 skip() 来跳过"到所需的匹配项并返回.

Use skip() to "skip" to the desired match and return that.

这是从这个SO answer修改而来的片段:

Here's a snippet as modified from this SO answer:

// Get the count of all users
User.count().exec(function (err, count) {

  // Get a random entry
  var random = Math.floor(Math.random() * count)

  // Again query all users but only fetch one offset by our random #
  User.findOne().skip(random).exec(
    function (err, result) {
      // Tada! random user
      console.log(result) 
    })
})

这篇关于如何在猫鼬中找到随机记录的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！