嵌套数组内的 MongoDB 查询

问题描述

我在 MongoDB 中有以下集合:

I have the following collection in MongoDB:

{
  "id": 123,
  "profile":{
    "name": "name",
    "age":45,
    "wishlist": [
        {"_id":1, "name":"a1"},
        {"_id":2, "name":"a2"},
        {"_id":3, "name":"a3"}
      ]
  }
}

在 Mongo Shell 中查找 wishlist 是否有集合 where _id = 2 的查询是什么?

What is the query in the Mongo Shell to find if wishlist has collection where _id = 2 ?

推荐答案

当你只匹配 one 字段时，你只需要使用点符号表示你的字段的路径:

As you ony match against one field, you only have to express the path to your field using dot-notation:

> db.user.find({"profile.wishlist._id": 2})

如 MongoDB 文档，对于数组(如 wishlist)，如果数组中的任何 子文档与字段值匹配，则这将匹配文档.

As explained in the MongoDB documentation, for arrays (like wishlist) this will match a document if any subdocument in the array match the field value.

请注意，如果您需要匹配几个字段，则需要使用:

Please note that if you need to match against several fields, you need to use either:

• $elemMatch 如果所有匹配的字段都应该属于相同子文档；
• 或多个字段，如果各个字段不需要匹配同一个子文档，则使用点符号表示.

• $elemMatch if all matching fields should belong to the same subdocument;
• or multiple fields expressed using the dot-notation if the various fields don't need to match against the same subdocument.

请比较这两个查询的输出以了解这一点:

Please compare the output of those two queries to get a grasp on this:

> db.user.find({"profile.wishlist._id": 2, "profile.wishlist.name": "a1"})
//                                      ^                            ^^
//                              will return your document even if the was no
//                              subdocument having both _id=2 and name=a1

> db.user.find({"profile.wishlist": {$elemMatch: { _id: 2, name: "a1"}}})
//                                                      ^         ^^
//                                         no result as there was no subdocument
//                                         matching  _both_ _id=2 and name=a1

这篇关于嵌套数组内的 MongoDB 查询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！