如何使用elemMatch匹配嵌套数组

问题描述

我有一些这样的数据结构

I have some data structure like this

{
  a: 1,
  array1: [
    {
      b: 2
      array2: [
        { 
          // this is my target
          c: 3,
          d: 3
        },
        {
          c: 4,
          d: 4
        }          
      ]
    },
    {
      b: 3
      array2: [
        {
          c: 5,
          d: 5
        },
        {
          c: 6,
          d: 6
        }          
      ]
    }
  ]
}

我知道使用{"array1" : {"$elemMatch" : {"b" : 2} } }来匹配第一级array1的元素.但是我不知道如何匹配array1的array2的元素{c: 3, d: 3}.

I know use {"array1" : {"$elemMatch" : {"b" : 2} } } to match element of first level array1. But I don't know how to match element {c: 3, d: 3} of array2 of array1.

推荐答案

$elemMatch用于声明同一嵌套结构内多个字段之间的关联.

$elemMatch is used to state association among multiple fields within the same nested structure.

例如如果要查询c和d并需要它们属于同一子文档，则可以像这样查询它.

For eg. If you are looking to query c and d and need them to belong to the same sub-document, the you can query it like.

{"array1.array2" : {"$elemMatch" : {"c" : 3, "d":3} } } 

注意:如果要查询单个字段，则实际上不需要使用$elemMatch(因为没有关联)

Note: if you are querying on a single field, you dont really need to use $elemMatch (since there is no association)

例如，在您的查询示例中，您可以代替

For instance, in your query example, you can instead do

{"array1.b" : 2} 

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