Mongo用未知的父键查找值 [英] Mongo find value with unknown parent key

问题描述

我在 Mongo 表中寻找一个值，该值的父键可能没有描述性或已知名称.这是我们的一个文档的示例.

I am looking for a value in a Mongo table where its parent key might not have a descriptive or known name. Here is an example of what one of our documents looks like.

    { 
       "assetsId": {
         "0": "546cf2f8585ffa451bb68369" 
      },
       "slotTypes": {
         "0": { "usage": "json" },
         "1":  { "usage": "image" }
      }
    }

我想看看这是否在 slotTypes 中包含 "usage": "json"，但我不能保证此用法的父键为 "0".

I am looking to see if this contains "usage": "json" in slotTypes, but I can't guarantee that the parent key for this usage will be "0".

我尝试使用以下查询但没有任何运气:

I tried using the following query without any luck:

db.documents.find(
   {
     slotTypes:
       {
          $elemMatch:
            {
               "usage": "json"
            }
       }
    }
)

如果这是一个非常基本的问题，请提前抱歉，但我不习惯在 nosql 数据库中工作.

Sorry in advance if this is a really basic question, but I'm not used to working in a nosql database.

推荐答案

我不确定你是否能够用你当前的模式优雅地解决这个问题；slotTypes 应该是一个子文档数组，这将允许您的 $elemMatch 查询工作.现在，它是一个带有数字键的对象.

I'm not sure you're going to be able to solve elegantly this with your current schema; slotTypes should be an array of sub-documents, which would allow your $elemMatch query to work. Right now, it's an object with numeric-ish keys.

也就是说，您的文档架构应该类似于:

That is, your document schema should be something like:

{
   "assetsId": {
     "0": "546cf2f8585ffa451bb68369"
  },
   "slotTypes": [
     { "usage": "json" },
     { "usage": "image" }
  ]
}

如果无法更改数据布局，那么您基本上需要扫描每个文档以找到与 $where 匹配的内容.这很慢，无法编入索引，而且很笨拙.

If changing the data layout isn't an option, then you're going to need to basically scan through every document to find matches with $where. This is slow, unindexable, and awkward.

db.objects.find({$where: function() {
  for(var key in this.slotTypes) {
    if (this.slotTypes[key].usage == "json") return true;
  }
  return false;
}})

您应该阅读 $where 上的文档 以确保您了解它，以及对所有神圣事物的热爱，净化您对该功能的输入；这是在您的数据库上下文中执行的实时代码.

You should read the documentation on $where to make sure you understand the caveats of it, and for the love of all that is holy, sanitize your inputs to the function; this is live code that is executing in the context of your database.

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